The Senate vote to recommend that Brett Kavanaugh be confirmed to the vacant seat on the US Supreme Court had appeared to be an inevitability.
The 11 Republicans and 10 Democrats had already signalled they would stick to party lines and send Judge Kavanaugh's nomination for a full vote in the Senate in the coming days.
But the change of heart of Arizona senator Jeff Flake, a Republican who is retiring from the Senate this year, was pivotal in at least delaying the elevation of Judge Kavanaugh.
Mr Flake, often a vocal critic of his own party's president, had been outspoken in raising doubts about Judge Kavanaugh in the days leading up to this week's historic hearings.
But his original decision to swing his support behind Donald Trump's pick for the highest court in the land had prompted a swift and intense response.
The image of Mr Flake, cornered in a congressional lift, being berated by a number of women who said they themselves had been the victims of a sexual assault, was searing and unforgettable.
Did that change his mind? Or was it the pleading of his Democrat colleagues?
Either way, his agreement that the FBI should be allowed look again into Judge Kavanaugh's background and the allegations against him was a significant moment.
The battle lines had been drawn: most Republicans want to get Judge Kavanaugh quickly confirmed, all Democrats wanted to see that further examination of the allegations by Christine Blasey Ford and others.
Mr Flake and the other Republican swing senators, Lisa Murkowski and Susan Collins, will hear a lot from Americans about what they think ahead of that final vote in the Senate.
The bitter and nasty fight on Capitol Hill is nothing compared to the strength of feeling on the streets of America right now. The testimony of Dr Ford and Judge Kavanaugh has moved Americans and created engagement unlike anything the country the seen in recent years.
"Who do you believe?" is a question everyone is having to answer - and the political and cultural consequences for America are enormous.
What happens now? Analysis by US correspondent Amanda Walker
An FBI investigation or a failed final vote. In the end there was no contest for Republicans who had previously dismissed the idea as unnecessary.
What could the FBI possible deliver that we're not getting in the Senate judiciary hearings? The short answer - witnesses. People like Mark Judge, the other person Dr Blasey Ford alleges was in the room when she was assaulted.
There are now several potential outcomes. The FBI investigation - now approved by Donald Trump - could work in Kavanaugh's favour.
If it yields nothing then the Republicans can use the fact that it happened to influence and reassure swing voters that this was a legitimate considered process.
But if it bolsters Dr Blasey Ford's allegations it could be fatal for Kavanaugh, leaving even his most steadfast supporters in a very tricky position.
There is also the possibility of him withdrawing his nomination, but after his defiant testimony that feels unlikely.
A lot can happen in the course of a Washington week. It's almost impossible to predict where this might stand in 24 hours - let alone by the end of the week-long FBI investigation
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