In 2016, Pennsylvania was key to President Donald Trump’s victory. But in 2018, the state is shaping up to be ground zero for a likely Democratic wave.

The newly redrawn congressional map, which nixes some GOP-gerrymandered districts, is Republicans’ chief concern and completely out of their control. But the size of that Democratic wave will depend on whether voters in suburban areas, many of them Democrats who supported Trump in 2016, are wary of giving Republicans another mandate to govern.

The suburbs of major Pennsylvania cities like Philadelphia were trending Democratic even before Trump came onto the political scene. But as moderate Republicans are having an increasingly difficult time navigating Trump’s takeover of the GOP, many of the same suburban voters who propelled Trump to the White House have turned against Republicans in recent special congressional elections—namely in Pennsylvania’s 18th district, where Democrat Conor Lamb defeated Republican Rick Saccone in a district that Trump won by 20 points in 2016.

Perhaps more problematic for the GOP, the party is continuing to lose the advantage of incumbency in districts that lean left. Rep. Ryan Costello (R-PA) became the latest Republican to announce his retirement last week, leaving his party to defend his suburban Philadelphia seat in a year when Democrats need to flip at least two dozen seats nationwide to give the speaker’s gavel back to Nancy Pelosi. The Cook Political Report on Tuesday moved Costello’s district from a “toss-up” to “likely Democratic.”

In an interview, Costello warned that the 2018 elections represent—in particular for those who did not vote in 2016—the “first chance to protest” against the unified Republican government under the leadership of the president. That anger will be directed toward elected Republicans, he said, regardless of whether those lawmakers view Trump favorably.

“There’s going to be a group of voters who voted for the president that may not be pleased with job performance or view him favorably, and this will be their opportunity to consider voting against him—and they do that by voting against their Republican member of Congress,” Costello told The Daily Beast. “That’s not even a working hypothesis anymore. That’s reality.”

Those Republicans who have already called it quits are putting the blame squarely on Trump, and are warning of large-scale buyers’ remorse among the same Pennsylvanians who backed the president in 2016.

“Suburban Republicans are at much greater risk under this presidency. It’s not just in the suburbs of Philadelphia but in the suburbs of New Jersey and in Minnesota, Colorado, California, Florida and elsewhere … more traditionally suburban districts are clearly more vulnerable in this political environment,” Rep. Charlie Dent (R-PA), a moderate Republican who announced last year that he wouldn’t be seeking re-election to his Allentown-area seat, said in an interview.

While Costello cited the fact that his new congressional district makes it nearly impossible for any Republican to win there, in an interview on MSNBC he hinted that many of the same suburban voters who went for Trump aren’t prepared to reward the GOP with another win this time around.

“There’s no question that it was going to be tough in light of what’s happening in the suburbs across the country,” Costello said. “In my district … the local Democrats and the left has become more engaged and, candidly, more angry by the week as President Trump says things and does things which many Republicans, myself amongst them, from time to time do disagree with.”

The chaos surrounding the Trump White House 14 months into his presidency is presenting real problems for elected Republicans. Costello said he and his colleagues are routinely put into a bind whenever they want to condemn the president’s actions or words—risking drawing the ire of Trump’s base while at the same time taking heat from newly energized Democrats for not going far enough to distance himself from Trump. All the while, he added, Republicans are being forced to weigh in on the president’s alleged marital misdeeds, high-profile White House staff shake-ups, and other negative stories.

“We’re talking about porn stars and the president rather than tax policy or what we need to get done by the end of the year,” Costello said, referring to porn star Stormy Daniels’ allegations of an affair with Trump.

Trump defeated Hillary Clinton in 2016 largely due to his successes among those who traditionally voted Democratic in states like Pennsylvania, Michigan and Wisconsin. But this year, moderate Republicans who out-performed Clinton in their own districts are choosing to retire rather than risk becoming a political casualty at the hands of Trump.

Costello was re-elected in 2016 by 14 points even though Clinton won his district by one point. Clinton won Costello’s new district, under the congressional map ordered by the state’s supreme court, by 10 points. In other words, Costello was in trouble regardless of what’s happening on the national political stage.

“The reason that Democrats have done as well as they have in Pennsylvania in statewide elections, despite the fact that Republicans hold the legislature and the congressional delegation … is largely because the Philadelphia and Lehigh Valley suburbs have been trending Democratic,” Terry Madonna, the director of the Center for Politics and Public Affairs at Franklin and Marshall College, told The Daily Beast.

“The reason Trump won is he engaged the rural and small-town voters, many of them Democratic in the northeast and southwest in the old mining and and mill town parts of the state,” Madonna said.

Complicating matters further, it all comes at a time when Republicans on Capitol Hill are openly disagreeing about how to craft a November strategy that minimizes the expected damage to their congressional majorities.

Conservatives argue that the best way to counteract the groundswell of opposition against Trump, in the form of a massive Democratic wave, is to double down on the base—that is, keeping pushing conservatives legislative agenda items in order to give the GOP base a reason to vote in November.

“The people of this country came out by the millions to support Donald Trump, support his agenda and the policies that he’s pushing forward. And he has been delivering day in and day out on that front,” White House Press Secretary Sarah Sanders said on Tuesday. “I think the people that voted for and came out and supported him still do so.”

But moderates like Dent and Costello have said that playing to the base will further embolden Democratic opposition to Trump, leaving suburban Republicans in a difficult bind as they try to appeal to the same Democrats who voted for Clinton.

“That doesn’t mean Republicans in suburban districts can’t win. It just means that it’s a very catch-22 type of conundrum that we find ourselves in,” Costello said on MSNBC on Tuesday. “... I’ve lived through it for the last year and a half.”