Aggressive maneuvering by Senate Majority Leader Mitch McConnell and Republican voters’ overwhelming opposition to impeachment are conspiring to deliver President Trump a unanimous GOP vote of acquittal at his trial in the Senate.

That Senate Republicans are on track to acquit Trump and shield him from expulsion was not in doubt as the trial adjudicating two articles of impeachment opened on Tuesday. But, as House Democratic prosecutors and the White House defense team began litigating charges of abuse of power and obstruction of Congress, McConnell’s push for unity and grassroots loyalty to Trump were moving Senate Republicans behind the scenes toward unanimous acquittal.

“It wouldn’t surprise me to have all 53 Republicans” acquit, Sen. Josh Hawley of Missouri told the Washington Examiner. “If we’re voting based on the evidence, I think, clearly, we vote to acquit.”

Since Dec. 18, when House Democrats impeached Trump on a near party-line vote, new revelations emerged about White House dealings with Ukraine that might further substantiate allegations against the president. The information has not swayed most Senate Republicans, who, before hearing arguments in the well of the chamber, had confidently concluded that the case against Trump was flimsy.

Even as many GOP senators doubt the case on the merits, GOP insiders concede privately that key political factors are influencing Senate Republicans as they weigh Trump’s culpability. How compelling they find the prosecution’s argument and their assessment of Trump temporarily withholding $391 million in military aid to Ukraine while asking Kyiv to launch an investigation into political rival Joe Biden are secondary.

Impeachment has strengthened Trump’s hold on Republicans broadly. This development is as true in blue states and 2020 battlegrounds as in reliably GOP territory. Combined with Trump’s stable job approval numbers nationally and his uncommonly strong bond with the conservative base, the pressure to stick with the president is immense.

One Republican lobbyist said impeachment was such a significant party litmus test that the bar for breaking ranks is too high. “Bipartisanship and moderation can be achieved, but they can’t be achieved with threshold questions like this,” the source said.

If all 47 Senate Democrats vote to convict on conclusion of the trial, a prospect far from guaranteed, 20 Republicans would have to join with them for Trump to be removed from office. Since early in the House investigation last fall, it has been apparent the president is not in danger of this sort of large-scale defection.

McConnell has worked to maintain a united GOP front among members of his conference and with Trump. So far, the majority leader’s effort is paying dividends, beginning with the unanimous Republican support he won for the resolution determining how the impeachment trial will unfold.

The few who might entertain convicting Trump are experiencing peer pressure, however.

“It’s easier to vote on the merits if it’s going to matter,” said a Republican lobbyist with relationships in the Senate. “Otherwise, you’re just pissing in the wind.”

Underscoring the political concerns driving Senate Republicans, party strategists are not concerned about four of the five GOP incumbents whose reelection is in peril and stand to lose the most in November if they oppose impeachment.

Sens. Susan Collins of Maine, Joni Ernst of Iowa, Cory Gardner of Colorado, Martha McSally of Arizona, and Thom Tillis of North Carolina are the most threatened Republicans on the 2020 ballot. Only Collins is considered a possible “yes” vote to convict, but doing so would risk a backlash in the primary or general election by Republican voters.

The others to watch are Sen. Lamar Alexander of Tennessee, one of McConnell’s oldest friends, who is retiring this year, Sen. Lisa Murkowski of Alaska, and Sen. Mitt Romney of Utah. These three have maintained their neutrality throughout the process. Some GOP insiders suspect that most Senate Republicans will maintain the veneer of indecision only to vote with their party in the end, if not on the merits, then because of political considerations.