(Reuters) - President Donald Trump’s nomination of conservative federal appeals court Judge Brett Kavanaugh to the U.S. Supreme Court is likely to hinge on the votes of a handful of senators: three Republicans and two Democrats.

Slideshow ( 5 images )

The Senate on Thursday was reviewing an FBI report on allegations of misconduct by Kavanaugh that have jeopardized his selection for a lifetime seat on the nation’s highest court. [nL2N1WK07H]

It was not immediately clear if the report, seen already by some Democrats as inadequate, would satisfy senators who have concerns about Kavanaugh’s past, his character and temperament.

Any nominee to the Supreme Court must be approved by the Senate, where Trump’s fellow Republicans hold a 51-49 majority.

If all the Senate’s Democrats and independents were to oppose Kavanaugh, Trump could not afford to lose more than one Republican vote for his nominee, with Vice President Mike Pence casting a tiebreaking vote. That calculation would change if one or more Democrats were to vote in favor of Kavanaugh.

No Republicans have said they will vote against him, but three intervened in the confirmation process last week to demand closer scrutiny by the FBI of Kavanaugh’s past conduct.

Here are the five whose views will be crucial. A procedural vote could come on Friday and a final vote shortly after that.

REPUBLICANS

* Jeff Flake. He voted in favor of Kavanaugh at the committee level, but only after extracting a promise from other lawmakers that the FBI would look into the allegations against the nominee. It was unclear whether Flake’s final vote would be contingent on the FBI probe. He is not running for re-election and has been seen as a possible challenger to Trump in 2020.

* Susan Collins. A moderate who sometimes breaks from party ranks, Collins joined Flake in calling for additional FBI scrutiny. CNN on Thursday reported Collins as saying that the FBI probe “appears very thorough.”

* Lisa Murkowski. An occasional party renegade, she has not said how she will vote. She sided with Flake and Collins on the FBI probe. Murkowski on Wednesday described as “inappropriate” comments by Trump on Tuesday mocking university professor Christine Blasey Ford, who accused Kavanaugh of sexually assaulting her when they were high school students in 1982.

DEMOCRATS

* Joe Manchin. Facing a re-election vote in November in the pro-Trump state of West Virginia, he said on Friday he supported Flake’s call to delay voting so the FBI could investigate. Manchin has not said how he will vote on Kavanaugh.

* Heidi Heitkamp. Facing a re-election campaign in North Dakota, also a heavily pro-Trump state, she called even before Flake did for further investigation of Ford’s allegations. Five weeks before the Nov. 6 elections, Heitkamp faces a difficult decision. If she opposes Kavanaugh, she risks alienating conservative voters who support him. If she supports Trump’s nominee, she might provoke a backlash among core supporters that could depress Democratic turnout in her bid for a second term.