The 2024 presidential election is expected to be decided by slim margins across a handful of battleground states. And one former Republican staffer on Capitol Hill thinks former President Donald Trump needs to reverse course if he hopes to prevent disgruntled GOP voters from defecting to President Joe Biden’s camp.

When she suspended her campaign after the Super Tuesday primaries and caucuses, former UN ambassador Nikki Haley notably declined to endorse Trump, saying he would have to “earn” her supporters’ votes in November. And so far, Trump has not made any inroads with his former rival’s base. Tara Setmeyer, who was a communications director for a Republican member of Congress for seven years, recently told the Guardian that his refusal to court her supporters could cost him in November.

“Partisanship and loyalty to your tribe has become a very powerful tool and breaking away from that has been incredibly difficult for a lot of people,” she said. “But Donald Trump’s antics, rantings, continued extremism and attacks on women in particular are making it very difficult for those Haley voters to stay under the tent with Trump.”

READ MORE: Trump’s win in Georgia’s primary exposed what may be his fatal flaw in the must-win state

“It’s incredibly smart of the Biden campaign to begin planting the seeds to give Haley voters and swing state independent voters a permission structure to vote for him,” she continued.

Even though Trump won the Georgia Republican presidential primary by a wide margin last month, Haley’s vote share may have exposed a chink in his armor. The former South Carolina governor had already dropped out of the race by the time 77,000 GOP voters in the Peach State cast their ballots for her. And while many of those were early votes, approximately 22,000 Republicans voted for Haley after she suspended her campaign. And because Biden won Georgia in 2020 by less than 12,000 votes spread across all 159 counties, the data suggests he may win the swing state again with the help of Haley’s base.

“Trump has continued to get crazier and crazier,” Brookings Institution senior fellow Elaine Kamarck told the Guardian. “If he had been running a more normal campaign where he reached out to Haley voters, where he reached out to disaffected Democrats, it’s one thing, but instead he’s running a campaign that’s based on hatred and retribution and he’s more incoherent than ever.”

According to the Washington Post, roughly 17% of Republican primary voters have consistently cast protest votes for non-Trump candidates like Haley, Florida Governor Ron DeSantis and other former GOP candidates no longer in the running. In this week’s Republican primary in Wisconsin — another crucial battleground state — more than 76,000 voters selected Haley. Biden’s margin of victory in the Badger State in the last election was just over 20,000 votes, making it possible for him to win there in 2024 by engaging with Haley’s base.

READ MORE: ‘There is a place for them in my campaign’: Biden makes his case to Haley supporters

Trump and his surrogates have not only refused to reach out to Haley supporters, but have openly turned them away, along with her donors. After Super Tuesday, former White House chief strategist Steve Bannon said, “Screw Nikki Haley – we don’t need her endorsement.” And the former president said her financial backers were “permanently barred from the MAGA camp.

In the meantime, Biden has actively courted the former UN ambassador’s base, saying “there is a place for them” in his campaign. And CNBC reported in March that roughly half of Haley’s bundlers — heavy-hitting fundraisers who collect political contributions from numerous donors in chunks — have now flipped to Biden’s side.

“”It takes a lot of courage to run for president — that’s especially true in today’s Republican Party, where so few dare to speak the truth about Donald Trump,” the president stated after Haley ended her campaign. “Nikki Haley was willing to speak the truth about Trump: about the chaos that always follows him, about his inability to see right from wrong, about his cowering before Vladimir Putin.”

READ MORE: ‘Nikki Haley got trounced’: Trump mocks his former UN ambassador after she ends campaign