Sen. Joe Manchin (D-W.V.), one of the most vulnerable Democratic lawmakers up for re-election this year, knows that he has to placate President Donald Trump through November—even if the president doesn’t return the favor.

After Trump threw the conservative Democrat under the bus last week in an interview with The New York Times over the senator’s vote against the GOP tax bill, Manchin gave the president a call.

“I just assumed, Mr. President, that your staff has not made you aware of all the things I’ve done, all the meetings we’ve had, all the different correspondence back and forth of what we could find of a bipartisan pathway forward,” Manchin said he told Trump, detailing the conversation to The Daily Beast. “I just assumed that you weren’t told that and I would like from this day forward, on bills that we want to work in a bipartisan way—and I want to work every bill in a bipartisan way—and when you’re serious about a bipartisan bill that you want to work on too, then I’m going to come directly to you.”

Manchin indicated on Wednesday that he would continue extending olive branches to Trump, ostensibly as a means to shore up his re-election chances in a state that the president won by 42 points in 2016.

Trump unleashed on Manchin last week for voting against the tax bill in December, despite Manchin’s claims that he engaged in good-faith efforts with top administration officials in the early stages of the tax-writing process.

“You know, we hear bullshit from the Democrats. Like Joe Manchin. Joe’s a nice guy,” Trump told the Times. “But he talks. But he doesn’t do anything. He doesn’t do. ‘Hey, let’s get together, let’s do bipartisan.’ I say, ‘Good, let’s go.’ Then you don’t hear from him again. I like Joe. You know, it’s like he’s the great centrist. But he’s really not a centrist. And I think the people of West Virginia will see that.”

Trump’s remarks put Manchin and a handful of his colleagues in an increasingly difficult position. Manchin, along with Sens. Heidi Heitkamp (D-N.D.), Joe Donnelly (D-IN) and Claire McCaskill (D-MO), will need to show a willingness to reach across the aisle in order to win over the majority of voters in their respective states, each of which Trump won overwhelmingly in 2016. But the perils of trying to work with the White House might outweigh the ostensible political benefits, as they risk unleashing the wrath of an unpredictable president’s whims.

Behind Trump’s disparaging remarks about Manchin is the president’s anger that the senator, along with his fellow moderate Democrats, could not be sold on massive tax cuts that they largely support. Heitkamp, who traveled on Air Force One with Trump for a tax reform event in North Dakota in September, said she was promised a better process for writing the legislation, which was crafted by Senate Republicans in a way that it could get across the finish line with only GOP votes.

Manchin said last month that he met with top White House aides Marc Short and Gary Cohn in order to come up with a bipartisan product—but Manchin’s office, at the time, blamed Senate Republicans for not involving them in the process. He said his impression from his phone call with Trump, though, was that this information “wasn’t flowing to [the president],” which in turn spurred Trump’s furor in his interview with the Times.

But in West Virginia, Trump’s words carry significant weight, and it does Manchin—the Senate’s most conservative Democrat—no favors to have the wrath of Trump directed his way in a state where the president remains popular. According to the most recent polling data out of the state, Trump’s approval rating stands at 59 percent, the second highest of any state. Manchin—whose approval rating is just below Trump’s at 53 percent—is pledging to stay the course, despite Trump’s attacks.

“It never makes it harder for me,” Manchin said when asked if Trump’s comments make it more difficult for him to vote alongside the president this year. “I always want to work with the executive branch, with the president, and with my Republican colleagues in the most productive way. And I think you have to be honest about that. I’ve said I’ve never been against something because I’m against it for political reasons.”

Those who know Manchin best don’t expect him to change in the face of Trump’s missives, either. Steve Farmer, a Republican lawyer in Charleston, W.V., who has known Manchin for nearly 30 years, advised the senator to ignore Trump’s attacks.

“If Trump wants something positive for West Virginia, Manchin will support it regardless of what the president says about him personally,” Farmer told The Daily Beast. “He can’t control the president’s behavior—he can only control his own.”

In Missouri, where McCaskill faces an uphill battle to win another term, Trump defeated Clinton by 19 points in 2016—but in the same year, Sen. Roy Blunt (R-MO) edged out his Democratic opponent by just three points. McCaskill, therefore, is being pushed to show Missourians that she is willing to embrace Trump and vote with Republicans in Congress on top agenda items this year.

“McCaskill has to do something to change the dynamic because a ‘normal’ cycle means she loses,” Ed Martin, a Trump surrogate and the former chairman of the Missouri Republican party, told The Daily Beast. “It’s got to be something Missourians can recognize. Immigration is unlikely. Tax reform is too late. Infrastructure seems a good option.”

But some argue that the GOP’s brand under Trump is so toxic that it would be political suicide for Democratic lawmakers to line up with Trump on any issue—even initiatives like infrastructure projects which many Democrats support. The president’s unpredictability, they contend, will hurt the Democratic party more than it will help, and Trump has proven himself to be an unreliable legislative partner.

“At the start of last year they had a chance to work with these [Democrats], but they blew it,” Jim Manley, who served as senior communications adviser to former Senate Majority Leader Harry Reid (D-NV), told The Daily Beast. “The president and his team are so bad at dealing with Congress, they should be sued for legislative malpractice. And so here we are. The only people scared of Trump are Republicans. Democrats are feeling no pressure to cut deals just for the sake of bipartisanship.”

Recent history, though, suggests that a strategy of embracing and touting bipartisanship can work for a vulnerable incumbent. In 2016, Sen. Pat Toomey (R-PA) ran an ad featuring former President Barack Obama’s praise of his push for his legislation, co-sponsored with Manchin, to expand background checks for gun sales—a move that drew the ire of the former commander-in-chief. Toomey was, at the time, running for re-election in a state that went for Obama in 2008 and 2012, and was thought to be reliably in Hillary Clinton’s corner.

“Getting things done for the people you represent is a good enough incentive” to work with the president of an opposing party, Toomey told The Daily Beast on Wednesday. “Serving your constituents is the reason that you ought to look for opportunities to do good things.”

Trump won Pennsylvania and Toomey defeated his Democratic opponent, Katie McGinty, to win re-election.