Senate GOP incumbents brace for MAGA primary challengers

Several GOP Senate incumbents are already staring down the threat of primary challenges next year as friction builds between the MAGA and establishment wings.

Sen. John Cornyn (R-Texas), who plans to run for reelection in 2026, is facing a possible primary challenger in Texas Attorney General Ken Paxton, a longtime ally of President-elect Trump. Meanwhile, Sen. Bill Cassidy (R-La.), who voted to convict Trump in his 2021 impeachment, has already drawn a MAGA challenger. Sen. Thom Tillis (R-N.C.), who was censured by his state party in 2023, could also face a tough fight from the right. 

These vulnerable GOP senators will have to walk a tightrope in supporting some of Trump’s most controversial Cabinet picks and pieces of legislation while also seeking to appeal to the broader electorates in their home states.

“The senators who are up this time around have watched the MAGA movement grow and understand that the tough votes they take today could be primary challenges tomorrow,” said Republican strategist Ron Bonjean, a former top spokesperson in the Senate. 

“They’ve seen the political combat Trump made, and his historic sweep of a Republican Congress and White House. And senators who are on the fence of particular issues will definitely be weighing that strongly: what their backyard looks like, how strong the MAGA base is at home,” Bonjean said. “It’s probably even stronger now.”

Republicans won control of the White House and both chambers of Congress last year as much of the country shifted rightward. But congressional control will be on the table again in 2026, as a third of the upper chamber’s seats go up for reelection. Republicans will be on defense in 20 states, compared to 13 states for Democrats.

On the heels of Trump’s win, the GOP Senate incumbents expected to be the most vulnerable next fall are those who voted to convict Trump in his 2021 impeachment trial or have signaled they might go against his second-term Cabinet picks. 

“The threat of primaries, I think from Trump's perspective, is real. It's a way to keep members in line,” said Brian Darling, a Republican strategist and former counsel for Sen. Rand Paul (R-Ky.).

Tillis, who kicked off his reelection bid in battleground North Carolina last month, is among those seen as possible obstacles to Trump’s Cabinet nominees after expressing reticence about former Rep. Matt Gaetz (R-Fla.), Trump’s now-withdrawn pick for attorney general, and Pete Hegseth, Trump’s nominee for Defense secretary. 

Tillis was also censured by the North Carolina GOP in 2023 over his support for policies that some said weren’t aligned with conservative values.

Sen. Joni Ernst (R-Iowa) is also seeking a third term in 2026 amid scrutiny over her questions about Hegseth. Last month, conservative media personality Charlie Kirk warned that Ernst shouldn’t “be surprised” about a primary challenge if she flouts the president-elect’s agenda.

“I don't think not supporting a nominee is going to make or break your primary,” Bonjean said. “But it's going to be a track record of [a] high-level no vote, high-level votes against the Trump administration.” 

Over in Louisiana, Cassidy hasn’t officially announced he’ll run for a third term but has still drawn an official challenge from Louisiana Treasurer John Fleming, who argued the senator’s vote to convict Trump in connection with the Jan. 6, 2021, attack on the U.S. Capitol “failed” the Pelican State. 

If Cassidy also goes against some of Trump’s Cabinet picks, Darling said, “he’s going to be begging” for a competitive primary fight. 

Tough primaries in already-red states like Iowa and Louisiana don’t necessarily mean the GOP is at risk of losing seats, but they could signal that those seats might shift rightward.

As Cornyn plans to try for his fifth term in the Senate, speculation is swirling about whether the Texas attorney general, Paxton, could try to oust him. Cornyn is seen as representative of the state GOP’s old guard, while Paxton is seen as a leader of the state’s rising far-right wing. 

Republicans do face more of a risk of losing a seat in Maine, where Sen. Susan Collins (R), who plans to run for her sixth term, has never faced a primary challenger but won by single digits last cycle. Vice President Harris beat Trump in Maine by 7 points in November.

This fact could give Collins more breathing room when it comes to backing Trump’s Cabinet picks, said Michael Zona, a Republican strategist and former aide to Iowa Sen. Chuck Grassley (R).

Otherwise, whether Trump supports a candidate is “more determinative than any other factor” as 2026 approaches, Zona told The Hill in a statement. 

“Senators who haven’t been supportive of President Trump in the past, and especially over this next year, are at risk of losing renomination,” Zona said. “The best these senators can hope for is that he remains silent in their race. That’s a huge gamble and I wouldn’t bet on those odds. For these senators, one has to imagine they are engaged behind the scenes to mend their relationship with the president.”

Looming exits and potential retirements could also complicate the numbers game for the GOP next year. Some observers have their eyes on Sen. Mitch McConnell (R-Ky.), 82, who has butted heads with Trump in the past and has not yet said whether he’ll run for another term.

JD Vance, the incoming vice president, officially resigned his Senate seat representing Ohio last week. The Buckeye State’s Gov. Mike DeWine (R), who reportedly met with Trump at Mar-a-Lago last month, will appoint his replacement. 

Sen. Marco Rubio (R-Fla.),Trump’s pick for secretary of State, will also vacate his seat if confirmed, with speculation swirling for weeks over whom Florida Gov. Ron DeSantis (R) might choose to take that seat.

There’s also the chance for GOP pickups. 

National Republican Senatorial Committee spokesperson Joanna Rodriguez pointed to two Democrats, Sens. Jon Ossoff (D-Ga.) and Gary Peters (D-Mich.), who are up for reelection in states where Trump edged out Harris.

“Our incumbents and challengers are committed to working with President Trump and his administration to restore the prosperity, security, and peace through strength Americans crave,” Rodriguez said in a statement. 

The Senate Republicans’ campaign arm has historically supported incumbents against primary challenges, and the group is expected to keep up that policy in 2026. 

“Midterm elections tend to be not great for the party in power,” Darling said, and ousting an incumbent senator in a primary is also no easy task. 

But Trump is “kind of a different leader,” Darling said, in that his first-term midterms saw Republicans pick up seats in the Senate, despite losing control of the House.  

“It's going to be tough. It's going to be a difficult cycle. This is a great test to see if the Trump realignment is going to hold forth.”