Donald Trump has weathered storm after storm throughout his presidency, emerging virtually unscathed from controversies and disasters thanks to a Republican firewall that has so far wholly insulated him from consequences. But new polling suggests that his support may be cracking amid the Ukraine scandal that has engulfed his presidency and sent him on a path toward impeachment. A Washington Post/Schar School poll released Tuesday found that public opinion is dramatically shifting in favor of the fast-moving impeachment inquiry Democrats launched in response to Trump’s attempt to get Ukraine to investigate Joe Biden. Fifty-eight percent of Americans surveyed said they support the probe, and close to half of respondents backed Trump’s removal from office. More troubling for Trump, nearly 30 percent of Republicans polled said they support the inquiry, and close to a fifth of registered GOP voters say he should be removed.

That’s an ominous sign for Trump, whose support among Republicans has already seemed more tenuous during this impeachment push than at perhaps any other point in his presidency. Lindsey Graham, Jim Jordan, and other usual suspects have come to his aid, but their efforts to downplay the allegations at the heart of the impeachment inquiry have come up embarrassingly short. And while only a few in the GOP have outwardly criticized the president’s actions, the silence from the majority of Republican lawmakers has spoken volumes. Republicans who are normally enthusiastic in defending the president have kept their distance, lacking a coherent strategy and wary of getting involved when practically every day brings new disturbing reports.

Trump’s erratic conduct hasn’t helped matters, making some Republicans uneasy with things like threats of civil war. If his daily ranting about a deep state conspiracy hasn’t rankled Republicans, his stunning decision to allow Turkey to invade Northern Syria, leaving America’s Kurdish allies exposed, certainly has. That reckless move drew bipartisan backlash, including from Graham, who called the decision Monday a “disaster in the making.”

With a Democratic majority in the House, it’s likely that Trump will eventually be impeached. That’ll blemish his “resume”—something he’s reportedly told Republicans he doesn’t want—but until recently didn’t seem like something that could result in his removal from office, given the tight grip he’s held on the Republican-controlled Senate. Conviction remains a long shot, even though he’s admitted to, and publicly doubled down on, the very things he was accused of in the whistleblower complaint that set this whole impeachment push into motion, but it no longer necessarily seems impossible. Republican lawmakers have been reluctant to turn on Trump out of fear that doing so could put their own political futures in jeopardy. But if public opinion continues to go against the president, that could give them cover to hold him accountable.

Already an impeachment campaign appears to be brewing behind closed doors in the Senate, with Mitt Romney, who’s been sharply critical of the president since the Ukraine scandal broke, said to be reaching out to GOP colleagues about potentially pushing to oust Trump. “He could have tremendous influence in the impeachment process as the lone voice of conscience in the Republican caucus,” a Romney adviser told my colleague Gabriel Sherman on Monday, noting that the Utah Senator could potentially rally Trump-skeptics like Susan Collins, Ben Sasse, and Cory Gardner to the impeachment cause. That still wouldn’t be enough to seal Trump’s fate in the Senate—two-thirds are needed to convict—but House Democrats’ inquiry has only just begun. Last week, one witness yielded a trove of damning text messages between Trump envoys and Ukraine that suggested military aid and a White House visit for Volodymyr Zelenksy would be contingent on opening a probe into the former vice president and his son, Hunter Biden; as the investigation continues, more revelations could emerge that further turn public opinion against Trump.