WASHINGTON - Democrats will need at least 17 Republican senators to break ranks to convict President Donald Trump after he was impeached on Wednesday, a high hurdle that would require changing the minds of lawmakers who have stood behind him.
That is more than the 10 House Republicans who broke with the president in the most bipartisan impeachment vote in American history, which charged Trump with incitement of insurrection.
Even as Republican Senate Leader Mitch McConnell publicly flirts with supporting a conviction for Trump's role in a deadly attack on the Capitol that targeted him and his staff, getting a third of the GOP Senate caucus to vote to convict will be no easy task.
Trump maintains high approval rating and a passionate following among some Republican voters. He still held a 71 percent approval rating with GOP voters in a Quinnipiac poll taken after the riot.
Convicting Trump would allow the Senate to bar him from ever seeking elected office again, instantly reshaping the 2024 Republican presidential primary in which he could otherwise be a candidate.
But impeachments are inherently political affairs and even a trial that takes place after Trump's term expires would be rife with political calculations, both for senators who could seek re-election and for those who might make a bid for the presidency themselves.
Republicans control the Senate now, but Democrats are set to take over after President-elect Joe Biden takes the oath of office as the new president on Jan. 20. A drawn-out trial could impede Biden's early days in office, which may be a feature or a bug for different senators.
Once the Senate seats all the newly elected members, the chamber will split 50-50 and incoming Vice President Kamala Harris will cast the tie-breaking vote.
A handful of Republican senators have already criticized Trump and signaled they would be open to support impeachment. But to secure a conviction, more votes would be needed and supporters would likely look to senators who are retiring or other long-time members who are viewed as institutionalists.
But that's likely to be difficult.
The outcome could come down to McConnell, who has a deep reservoir of trust within his caucus. If he were to back conviction, he could lead more reluctant senators to follow suit.
But for now, the Kentucky Republican says he is undecided.
"I have not made a final decision on how I will vote, and I intend to listen to the legal arguments when they are presented to the Senate," he wrote to colleagues on Wednesday afternoon, according to a spokesman.
McConnell and Trump have a complicated relationship - polar opposites in personality, staunch allies in some policy objectives. McConnell broke with Trump last week, making an impassioned plea to reject the president's efforts to overturn the election.
McConnell is in no rush to hold a trial; his office indicated he won't bring the Senate back before Jan. 19. That means the trial is all but guaranteed to conclude under a Biden presidency and Democratic-controlled Senate.
The factions in an impeachment trial
Liam Donovan, a lobbyist and former Senate Republican campaign operative, said McConnell's apparent willingness to consider conviction "suddenly turns an unthinkable break with Trump into something that is very much in play."
"I remain a skeptic, if only because 17 is still a daunting number," Donovan said. "McConnell's imprimatur alone would carry a ton of weight."
Utah Sen. Mitt Romney is seen as the most likely Republican to support conviction, as he was the only member of his party who voted to remove Trump from office in the first impeachment trial last year. In addition, Alaska Sen. Lisa Murkowski and retiring Pennsylvania Sen. Pat Toomey have said Trump should resign. Centrist Maine Sen. Susan Collins could be a supporter of conviction, as could Nebraska Sen. Ben Sasse.
After those five, it gets trickier.
One group could be octogenarian institutionalists who may be eyeing retirement: Iowa Sen. Chuck Grassley, Alabama Sen. Richard Shelby and Oklahoma Sen. James Inhofe.
Other targets may be senators who have been critical of Trump for trying to overturn the election, including Ohio Sen. Rob Portman and Louisiana Sen. Bill Cassidy. Retiring North Carolina Sen. Richard Burr is another possibility.
That still wouldn't be enough.
Two wild cards are Utah Sen. Mike Lee of Utah and Kentucky Sen. Rand Paul. They have presented themselves as "constitutional conservatives" and were unwilling to vote with Trump to overturn the election even before the riot breached the Capitol. But both have been very supportive of Trump and Paul is facing voters in deep-red Kentucky next year.
The critical question, then, is how hard McConnell would push fellow Republicans to vote to convict - and how many would be willing to follow him. Two members of his leadership team, Missouri Sen. Roy Blunt and South Dakota Sen. John Thune, face re-election in 2022 and would risk a primary challenge.
Two others, Sen. Joni Ernst of Iowa and Sen. Todd Young of Indiana, have more time before they'll face voters again and might be more inclined to follow McConnell.
McConnell's position might also command votes from rank-and-file senators like North Dakota Sen. Kevin Cramer and South Dakota Sen. Mike Rounds. But the highly charged politics and deep fracture shaking the GOP may scramble any typical calculation.
One senior Republican aide told NBC News the votes will probably be there to convict Trump if McConnell is on board. But a former Senate GOP staffer said he may need to work for it.
"If McConnell were to say 'I'm voting to convict' but this is a conscience vote, it's still hard to get to 17. He would need to work it," said the former aide, who maintains relationships with ex-colleagues and offered a candid assessment on condition of anonymity. "This is a situation where you could have an easy 10 votes. But 11 to 17 is probably harder."