The sex-crimes prosecutor Republicans hired to question Brett Kavanaugh and accuser Christine Blasey Ford at Thursday's hearing told senators the case would not hold up in a courtroom, sources told Fox News—guidance that could prove critical as wavering lawmakers prepare to vote.

The prosecutor, Rachel Mitchell, spoke at an overnight meeting where all 51 Republican senators were present, two people briefed on the session said.

“Mitchell spelled it out and was clear with senators that she could not take this anywhere near a courtroom,” one source told Fox News. She told them she would not charge the Supreme Court nominee and reportedly said she wouldn't even seek a search warrant.

Mitchell’s opinion could sway fence-sitting senators ahead of a critical Senate Judiciary Committee vote set for Friday afternoon.

It is not necessary for Kavanaugh to secure majority approval of the committee in order to advance to the full Senate, but a favorable recommendation could bode well for his imperiled nomination -- and vice-versa.

In a critical development, Republican Sen. Jeff Flake announced Friday morning he will support Kavanaugh, saying, "I left the hearing yesterday with as much doubt as certainty."

With that, 48 Republican senators have now pledged to vote for Kavanaugh at the scheduled full Senate vote on Tuesday. The outstanding Republicans are Sens. Susan Collins of Maine, Lisa Murkowski of Alaska, and Mike Enzi of Wyoming. Enzi is expected to vote in support of Kavanaugh, but has said he won’t announce his position until he votes.

But Collins, Murkowski, Flake and Democratic Sen. Joe Manchin could vote in a bloc. The source told Fox News that Collins, Murkowski and Flake huddled with Manchin on the sidelines Thursday evening to discuss the nomination, right before the GOP lawmakers were briefed by Mitchell. They spoke for approximately 30 minutes.

“It’s a tough one. She offered good testimony, and so did he,” Flake, who sits on the Judiciary Committee, said Thursday night, before announcing his support. “If you’re making an allegation, you want there to be some corroboration. Where is the burden? It’s like impeachment. You don’t know.”

Republicans, including President Trump, have stressed that none of the sexual misconduct allegations against Kavanaugh made in the last several days have first-hand corroboration.

But Ford insisted during Thursday's testimony that Kavanaugh and a friend trapped her in a room during a high school gathering in 1982, and the now-court nominee tried to force himself on her before she escaped. She said she's "100 percent" sure it was him, though Kavanaugh adamantly denied it.

Asked whether more time or investigating would help, as Democrats suggested repeatedly on Thursday, Flake rejected the idea.

“Where does this start, where does it end?” he asked. “More time, more ludicrous allegations. What does that do to the accused?”

Manchin, from deep-red West Virginia, is seen as a possible "yea" vote for Kavanaugh.

“There have been no decisions,” Manchin reportedly said outside the hearing room. “There are some concerns that people have, and we’re going to try to close that loop.”

Democratic Sens. Heidi Heitkamp of North Dakota and Joe Donnelly of Indiana also have not revealed which way they might vote.

Early Friday, Sen. Bill Nelson, D-Fla., said that he would vote “no.”

Republicans hold a narrow 51-49 majority in the Senate, and can only afford one defection in their bid to confirm Kavanaugh, assuming they secure no Democratic votes.

Other Republican senators whose votes were expected to be up in the air, like Sens. Bob Corker, came out in support of Kavanaugh late Thursday.

“While both individuals provided a compelling testimony, nothing that has been presented corroborates the allegation,” Corker said in a statement, referring to Kavanaugh and Ford.

Kavanaugh vehemently denied the allegations leveled against him by Ford, calling the process a “national disgrace” and a “circus.”

“The Constitution gives the Senate an important role in the confirmation process,” Kavanaugh said in his opening statement. “But you have replaced advise and consent with search and destroy.”

Senate Majority Leader Mitch McConnell, R-Ky., announced late Thursday a full Senate vote for Tuesday.

“I think we’re going to go ahead,” Sen. Orrin Hatch, R-Utah, said. “I worry about every one of these votes.”

Fox News' Chad Pergram and Gregg Re contributed to this report.