The Race
Indiana State Senate District 25 covers all of Madison County and a portion of Hamilton County, anchored by the city of Anderson (population roughly 54,000). The district has approximately 135,806 residents and leans solidly Republican. In 2022, incumbent Mike Gaskill won with 64.1% (23,967 votes) over Democrat Tamie Dixon-Tatum's 35.9% (13,447 votes). Trump carried Indiana statewide by roughly 19 points in 2024, and Madison County's margins ran significantly redder than the state average. [1]
The May 5, 2026, primary features contested races on both sides -- two Republicans and two Democrats -- which is unusual for a district where past primaries have often been uncontested or low-profile. The Republican winner is the overwhelming favorite in the November general election.
What makes SD-25 distinctive in the 2026 cycle is not its competitiveness -- the seat is safe Republican territory -- but the convergence of three separate threads: Trump's endorsement of the incumbent as a reward for supporting redistricting, a party-discipline fight over a challenger declared "not in good standing," and a veteran Democratic candidate making her third consecutive run for the seat.
Republican Primary
Mike Gaskill (Incumbent, Trump-endorsed)
Insurance agent, Pendleton, first elected 2018
Mike Gaskill is not merely a senator seeking reelection. He is the man who carried Trump's water on redistricting -- and got rewarded for it.
Gaskill grew up in Pendleton, graduated from Pendleton Heights High School, and earned degrees in accounting and computer science from Anderson University. He worked as a business systems manager at Praxair Surface Technologies before opening an insurance and financial services business in Anderson in 1993, which he still operates. Before entering state politics, he served on the South Madison Community School Board and the Madison County Council. [2]
He was first elected to the Indiana Senate in 2018, representing District 26 (Madison, Delaware, and Henry counties) with 57.8% in a three-way race. Following 2021 redistricting, his home moved into District 25, where he won a contested primary with 56.1% against Evan McMullen and then defeated Dixon-Tatum in the general with 64.1%. [3]
Gaskill chairs the Senate Elections Committee and serves on the Family & Children Services, Insurance and Financial Institutions, and Tax and Fiscal Policy committees. [2] That Elections Committee chairmanship put him at the center of the redistricting fight. He served as the Senate sponsor of HB 1032, the Trump-backed congressional redistricting bill, and used his committee to advance it to the floor. During debate, he showed senators maps of congressional districts around the country and used all 30 minutes of his allotted speaking time arguing for the bill. [4]
The bill went down 31-19 on December 11, 2025, with 21 Republicans joining all 10 Democrats to defeat it. [4] Gaskill was on the losing side -- but the losing side that Trump wanted. In March 2026, Trump endorsed Gaskill as one of 11 Republican senators who supported redistricting, calling them "MAGA WARRIORS" who "WILL NEVER LET YOU DOWN." [5]
Beyond redistricting, Gaskill made headlines in February 2026 by proposing to cut Indiana's early voting period from 28 days to 16 days through a committee amendment, with no public testimony allowed. Voting-rights advocates including Common Cause Indiana criticized the move, and the measure ultimately lacked Senate support to advance. [6]
Gaskill's campaign finance record is solid: $475,219 in total contributions across the 2018-2022 cycle, with $208,357 in expenditures. [3] He is the heavy favorite to win renomination.
Katherine Callahan
Nurse practitioner, Lapel, party-challenged primary candidate
Katherine Callahan's candidacy is less a conventional primary challenge than a case study in how Indiana's Republican Party disciplines its own.
Callahan holds a Doctor of Nursing Practice (DNP) degree from the University of Indianapolis and lives in Lapel, a small town in Madison County. Her public-sector experience includes serving as Chief Deputy Coroner of Madison County, a position she later resigned from. In 2024, she ran for Madison County Auditor in the Republican primary and lost to Todd Culp. She told the Herald Bulletin that her 18- and 21-year-old daughters pushed her into politics, giving her an ultimatum: run for office or stop complaining on social media. [7]
In February 2026, former Madison County Republican Party chairman Russ Willis filed a complaint against Callahan with the Fifth District of the Indiana Republican Party. The charge: supporting Democrats seeking public office. The Fifth District determined Callahan is "not in good standing" with the party. [8]
That phrase carries specific consequences under Indiana Republican State Committee Rule 1-25, which defines a "Republican in Good Standing" as someone who supports GOP nominees and does not "actively or openly support another candidate against a Republican nominee." A candidate found not in good standing cannot be removed from the ballot by party action alone -- that requires a separate statutory challenge. But the penalties include being barred from Republican party events and, critically, losing access to the party's proprietary voter database, a resource essential to any competitive campaign. [9]
Separately from the good-standing determination, the Madison County Election Board upheld challenges in late February 2026 to remove three candidates from the Republican primary ballot based on a statutory requirement: candidates must have voted in the party's two most recent primary elections or obtained a waiver from the county party chair. Whether Callahan was among those three is not confirmed from available reporting -- Ballotpedia continues to list her as a candidate for the SD-25 Republican primary as of March 30, 2026. [10]
Callahan did not complete Ballotpedia's candidate survey and has limited publicly available campaign platform information. Her candidacy appears to be rooted in local Madison County Republican faction politics -- the Willis complaint, the good-standing determination, and the broader pattern of five such complaints across Indiana in 2026 (the party upheld four of five) all suggest an internal party gatekeeping function rather than a substantive policy disagreement. [9]
Against a Trump-endorsed incumbent with a campaign war chest, committee chairmanship, and full party backing, Callahan faces essentially insurmountable odds.
Democratic Primary
Tamie Dixon-Tatum
Director of Civil Rights and Human Relations, City of Anderson
Tamie Dixon-Tatum is nothing if not persistent. This is her third consecutive campaign for SD-25 and her fifth overall run for office since 2018.
Her political career began when her father, Anderson City Councilman Ollie H. Dixon, withdrew from a challenge to incumbent Democratic senator Tim Lanane in the 2018 primary. Dixon-Tatum replaced him. The elder Dixon explained the choice bluntly: people "wanted a young, woman, minority candidate." She lost to Lanane 35.2% to 64.8%. [11]
In 2022, with Lanane retired and the seat redrawn, Dixon-Tatum won the Democratic primary with 62% over Aaron Higgins, then lost the general election to Gaskill 35.9% to 64.1% -- a 28-point margin. [12] In 2024, she attempted a gubernatorial bid but was removed from the Democratic primary ballot for insufficient petition signatures (filing 1,896 of the required 4,500). She then sought the lieutenant governor nomination at the Democratic convention, finishing third with 10.6% of delegate votes. [13]
Between campaigns, Dixon-Tatum has built a substantive professional record. She holds a B.A. in Telecommunications, a Master's in Public Affairs, and a Master's in Legal Studies. Since 2016, she has served as Director of the City of Anderson's Human Relations Department, investigating discrimination complaints and operating a mediation program. She is President of the Indiana Consortium of State and Local Civil Rights Agencies and has spearheaded the Ollie H. Dixon Back-To-School Picnic and Parade for nearly 25 years, providing school supplies for thousands of disadvantaged children throughout Madison County. [14]
Her professional background in civil rights enforcement is directly relevant to state legislative work -- more relevant, arguably, than her prior campaigns have been able to communicate in a district this Republican. The question is whether deep community roots and name recognition can offset a 28-point deficit from 2022, particularly in a primary where she now faces a credible Democratic challenger for the first time.
Todd Shelton
Senior lecturer, UAW veteran, disabled military veteran, Alexandria
Todd Shelton offers a different kind of Democratic candidacy -- one built on the manufacturing economy that once defined Madison County and the labor networks that accompanied it.
Shelton grew up outside Alexandria, near Anderson, and graduated from Highland High School. He went straight to the factory floor, working at Magnequench/General Motors as a production worker, committeeman, and bargaining committee member in UAW Locals 662 and 2209. When his facility closed and relocated overseas, he transferred to another GM plant in Fort Wayne -- an experience he cites as formative in understanding how trade policy affects working families. [15]
He subsequently enlisted in the U.S. Army, serving from 2004 to 2006 until sustaining an injury that resulted in a medical discharge. He is a disabled veteran who has navigated the VA system and advocates for veteran support. Using Chapter 31 benefits and the GI Bill, he earned both bachelor's and master's degrees from IUPUI (now Indiana University Indianapolis). For over a decade, he has served as a senior lecturer there, teaching technology, web development, and application design. He also runs a small family business producing freeze-dried foods and handmade goods sold at Indiana markets. [15]
Shelton's campaign platform emphasizes economic stability for working families, public education funding and trade education, workers' rights, healthcare access, affordable housing, and opposition to corporate consolidation. He frames himself as a candidate of lived experience -- factory worker, union member, veteran, teacher, small business owner -- rather than political ambition. [16]
There is one complication in Shelton's 2026 profile: he initially filed for the U.S. House IN-05 Democratic primary before withdrawing or being disqualified, with zero FEC contributions reported for that race. He subsequently pivoted to the SD-25 state senate race. [17] Whether voters view that as pragmatic flexibility or insufficient commitment to the district is an open question.
Shelton brings a demographic profile -- white, male, veteran, union -- that theoretically has crossover appeal in a district like SD-25. His platform speaks to the economic anxieties of the Anderson area, where GM's departure decades ago reshaped the community. Whether that profile translates into primary votes against Dixon-Tatum's deeper roots and name recognition will be tested May 5.
Why It Matters
Senate District 25 is not going to flip. The Republican nominee will win the general election. What makes this race analytically interesting is what it reveals about three separate political dynamics operating simultaneously.
First, the Trump endorsement as loyalty reward. Gaskill did not merely vote for redistricting -- he sponsored the bill and chaired the committee that moved it forward. The endorsement is a direct reward for maximum effort on Trump's behalf, even in defeat. It is the mirror image of the six retribution endorsements Trump issued against senators who voted no. Gaskill's reward and their punishment are two sides of the same coin.
Second, the good-standing mechanism as intra-party discipline. Callahan's candidacy -- whatever its merits -- was hobbled before it began by a party apparatus that can declare a candidate persona non grata, strip her access to voter data, and brand her as disloyal, all without removing her from the ballot. The complaint was filed by a former county party chairman against a woman accused of supporting Democrats. Whether the accusation is accurate is almost beside the point; the mechanism exists to deter anyone who might cross party lines and to signal that challenges to endorsed incumbents will not be tolerated. [9]
Third, the Democratic primary poses a genuine question about what kind of opposition works in deep-red territory. Dixon-Tatum brings institutional memory, community networks, and civil rights credentials. Shelton brings a union-veteran-educator profile with potential crossover appeal. Neither is likely to win the general election. But in a district where Anderson's post-industrial economy remains the defining reality, the choice between them reflects a broader Democratic debate about whether to lean into identity-based advocacy or economic populism in hostile terrain.
The May 5 primary will determine both nominees. The Republican primary is not competitive. The Democratic primary is a real contest -- small, low-turnout, and unlikely to produce a general election winner, but a meaningful test of two different theories about what opposition looks like when you know you are going to lose.