While McConnell has called it “laughable” to claim that Trump committed an impeachable offense, he’s also taken a few careful steps to insulate his caucus against a possible reversal. “If this is the ‘launching point’ for House Democrats’ impeachment process,” he said in a statement to Politico, “they’ve already overplayed their hand.” But he also told CNBC he’d have “no choice” under Senate rules but to take up impeachment articles and stopped short of blessing Trump’s conduct. In recent weeks he’s ordered a bipartisan Senate intelligence investigation, backed a resolution written by Senate Minority Leader Chuck Schumer demanding that the administration turn over the then-secret whistleblower report, and announced he’d been privately pushing the administration to release aid to Ukraine that had been held up before Trump’s phone call with that country’s president.

While no Senate Republican has yet said Trump should be impeached over Ukraine, what they have said suggests he might not have a solid wall behind him if damaging information continues to come out. Trump’s sometime rival Mitt Romney of Utah has called the president’s actions “troubling in the extreme.” Nebraska’s Ben Sasse, who criticized Trump as a candidate but has fallen in line since, said his colleagues shouldn’t rush to “circle the wagons” around the president. And Senate Intelligence Chairman Richard Burr of North Carolina has vowed to “get to the bottom” of what happened.

It would likely take a collapse in support for Trump among Republican voters to change GOP senators’ calculus. While polls show increasing approval among the public for impeachment, it’s come mostly from Democrats. The president’s approval rating among GOP voters remains above 80% in public polls, making any Republican senator’s defection a potentially career-ending decision.