Former President Trump and his allies are struggling to clear the Republican field in North Carolina’s wide-open U.S. Senate race and galvanize GOP voters around his preferred candidate, Rep. Ted Budd (R-N.C.).

Despite winning the former president’s endorsement early on, Budd has so far failed to become the runaway favorite in the GOP primary and has regularly trailed his chief rival, former Gov. Pat McCrory, in polling.

That set off an effort by Trump and Budd’s allies to nudge former Rep. Mark Walker (R-N.C.) out of the race by promising an endorsement if Walker runs instead for a Greensboro-area House seat. Walker insisted on Thursday, however, that he would stay in the Senate race for now, while he weighs other options.

“This has to be something in my heart, and I don’t know that it’s there yet,” Walker told The Associated Press, referring to his thought process on a potential run for the U.S. House. “I’m willing to consider it.”

He acknowledged that he had met with Trump to discuss a potential bid for North Carolina’s new 7th District. But he denied reports that he had committed to exiting the Senate race, saying that such accounts of his meeting with the former president just weren’t “factual.”

The GOP’s hope for a quick resolution to the nominating contest also appears further away than ever. The state Supreme Court moved this week to delay the March 8 primaries until May 17 amid legal challenges to the state’s new congressional and legislative maps.

That decision effectively extends the Senate primary fight for an additional two months, drawing out what has already become a bitter and expensive race for the GOP nomination to succeed retiring Sen. Richard Burr (R-N.C.).

“The way I see it, Walker has more time to make a decision, and McCrory and Budd have more time to bleed each other out,” one North Carolina Republican operative said. “I don’t know who that helps or hurts more, but it certainly makes the primary more expensive for everyone.”

In an interview with Politico, Walker said that the current legal fights over North Carolina’s new political maps also contributed to his decision to remain in the Senate race for the time being.

Republicans aren’t the only ones facing a competitive Senate primary in North Carolina. Former state Supreme Court Chief Justice Cheri Beasley and state Sen. Jeff Jackson are vying for the Democratic nomination, though they’ve so far avoided attacking one another directly.

The GOP primary, on the other hand, has gotten particularly vicious. McCrory and Walker have both hammered Budd for his ties to the Club for Growth, a conservative political action committee that has pledged to spend at least $10 million to boost Budd’s campaign, seeking to cast him as beholden to outside interests.

Meanwhile, Club for Growth’s super PAC has peppered the airwaves with ads targeting McCrory as a Trump critic, including one slamming him for supporting Mitt Romey in the 2012 presidential election. That ad also includes a clip from McCrory’s radio show in which the former governor accuses Trump of “destroying democracy.”

The group also sent out a mailer to North Carolina voters this week, dubbing McCrory a “fatally flawed general election candidate who is the one potential Republican nominee likely to hand Sen. Richard Burr’s seat to the Democrats and keep Chuck Schumer in charge of the U.S. Senate.”

For his part, McCrory has sought to fashion himself as a more traditional Republican candidate capable of appealing to many of the moderate voters who could determine the 2022 race for the Senate. He’s talked up his high name recognition, as well as his record of winning statewide before.

Both Budd and Walker, meanwhile, have hewed closely to Trump, while attacking McCrory as a career politician and highlighting his loss to Gov. Roy Cooper (D) in 2016, a year that proved largely successful for other Republicans.

Polling in the primary has been limited, though what few surveys there have been show McCrory in the lead, with Budd trailing in second place and Walker stuck in third. An internal poll commissioned by McCrory’s campaign in October showed him with a 15-point lead over Budd.

But a more recent survey commissioned by Club for Growth PAC last month showed a much closer race, with McCrory leading Budd 36 percent to 33 percent. A polling memo released by the group tied McCrory’s shrinking edge to the fact that more voters had become aware of Trump’s endorsement of Budd.

“As awareness of Trump’s endorsement continues to grow, Budd should pull ahead and build a lead over the better-known former Governor,” the memo reads.

Budd has also improved on his fundraising after being outraised by McCrory in the second quarter of the year. Between July and September, the two candidates were nearly even in fundraising, while Budd ended the quarter with a roughly $400,000 cash-on-hand advantage over McCrory.

Walker badly trails both Budd and McCrory in the money race. In the third quarter of the year, his campaign reported raising roughly $122,000, according to Federal Election Commission filings.

There’s no doubt among Republicans that the primary remains highly competitive. But the race also underscores the limits of Trump’s endorsement in his post-presidency, even as he works to maintain his status as the GOP’s most influential standard bearer.

While Trump’s endorsement has certainly given candidates like Budd a boost, especially among the former president’s ultra-conservative base, it hasn’t always proven to be the guarantee of success that Republicans once considered it to be.

In Alabama, for instance, Republican Katie Britt has significantly outraised her Trump-endorsed primary rival, Rep. Mo Brooks (R-Ala.), and recent polling shows her competing aggressively with the Alabama congressman.

And in Pennsylvania, Trump’s choice to succeed retiring Sen. Pat Toomey (R-Pa.) — Sean Parnell — suspended his Senate campaign last month amid a series of personal controversies, including allegations that he physically and verbally abused his estranged wife.

Some Republicans also point to Republican Glenn Youngkin’s victory in this year’s race for Virginia governor as evidence that voters are willing to look beyond the former president’s preferences. While Trump ultimately endorsed Youngkin, he didn’t do so until after the primary.

What’s more, Youngkin kept the former president at arm’s length throughout his general election campaign. While he was careful not to isolate Trump and his base, he never campaigned alongside him and often sought to cast himself as a more traditional Republican candidate.

“Every Republican candidate should want Trump’s endorsement. They should welcome his endorsement if they can get it,” one veteran Republican strategist who has worked on Senate campaigns said. “But there’s more to it now. A lot of voters who didn’t like Trump are back in play for Republicans now. It’s not as simple as him picking winners and losers.”