The long-awaited Senate vote on Brett Kavanaugh's Supreme Court confirmation may be delayed overnight on Saturday because Montana's Republican Senator Steve Daines has to go to his daughter's wedding.

On Thursday, Daines - who has pledged to vote in Kavanaugh's favor - revealed he would not be there to vote at the planned time on Saturday but will fly back after his daughter's nuptials in Montana to cast his vote on Sunday if the Republicans need him to.

'I'd come back after the wedding. It will probably be early morning. We're taking it a day at a time to see what happens,' he told CNN on Thursday.

It remains unclear how crucial his vote will be for Kavanaugh who stands accused of sexually assaulting three women as a teenager.

While Republicans hold a 51-49 majority, the votes of three moderate Republicans and red state Democratic Sen. Joe Manchin remain unknown.

If Daines is out there are 99 votes to be accounted for.

If every Democrat and Republican who has already stated their position stays that way, that would mean 48-47 against with four votes still to be decided.

The swing votes are red state Democrat Joe Manchin and Republicans Jeff Flake, Lisa Murkowsky, Susan Collins.

If Daines remains out it would take two of those votes turning 'no' to defeat the nominee.

Flake has not said how he will vote but he has revealed that his mind is made up.

On Thursday, previously undecided Dem. Senator Heidi Heitkamp revealed she would vote against him. While Republicans cannot delay the vote without the agreement of all 100 Senators, they can hold it open overnight in order for Daines to get back in time to cast his vote.

His intentions, however, are clear. On Thursday, he said he had even called Kavanaugh to tell him to let him know he would do what was 'needed' to get him 'over the line'.

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Republican Senator Steve Daines will be at his daughter Annie's wedding on Saturday and won't be able to vote on Kavanaugh confirmation this weekend. Annie is seen, right, with fiance Brad Moss

'I just spoke with Judge Kavanaugh. I gave him a call tonight.

'Because the news was out there that — about the wedding

'I said, "Judge Kavanaugh, I’m going to be there to vote for you as needed"', he said.

His absence from Saturday's vote was not of concern to some. Donald Trump Jr. said on Friday morning that he had been 'assured' by Daines, 'a good hunting/fishing buddy', that he had it 'covered'.

'Steve Daines is a good friend and hunting/fishing buddy and as far as his vote this weekend is concerned he tells me he has it covered.

'Coming from this man you can take that to the bank!' Trump Jr. said on Twitter.

While Flake has yet to announce his decision, protesters went to his Phoenix office on Thursday calling for him to vote 'no'.

He thwarted the proceedings of a senate judiciary committee last Friday by unexpectedly calling for the FBI to be given another week to investigate Dr. Christine Blasey Ford's testimony

Police ended up arresting two protesters who tried to meet with Flake's staff and then blocked the entrance to his office building after they were turned away.

Heitkamp had been quiet until Thursday when she finally revealed she was a no.

'The process has been bad,' Heitkamp told her home-state WDAY-TV. 'But at the end of the day you have to make a decision, and I've made that decision.'

The FBI completed a background check into claims that Kavanaugh sexually assaulted Christine Blasey Ford at a gathering in the 1980s, delivering findings that both Senate Democrats and Republicans believe bolsters their positions

FINAL FOUR: The senators who remain undeclared on Judge Kavanaugh's nomination include (clockwise from top left) Arizona Republican Jeff Flake, West Virginia Democrat Joe Manchin, Alaska Republican Lisa Murkowski and Maine Republican Susan Collins

'I will be voting no on Judge Kavanaugh.'

In a statement minutes later, Heitkamp said that '[i]n addition to the concerns about his past conduct, last Thursday's hearing called into question Judge Kavanaugh's current temperament, honesty, and impartiality.'

Senate Republicans and Democrats engaged in angry clashes Thursday over the quickly completed FBI background investigation into sex assault allegations against Brett Kavanaugh. The rushed investigation didn't appear to change any minds, but it will provide midterm election campaign fodder until November 6.

Heitkamp's decision complicates her re-election efforts in a state where President Donald Trump romped over Hillary Clinton, winning by nearly 36 percentage points.

It also brings the total of 'no' votes to 48, all Democrats. Republicans have the same number of 'yes' votes in their pocket. One Democrat and three Republicans are still undeclared.

Majority Leader Mitch McConnell told reporters Thursday afternoon that the FBI report 'did not corroborate any of the allegations against Judge Kavanaugh.'

He complained about the Democrats stalling for time, saying that 'there's no way anything we did would satisfy the Democrats. They've always got a reason why the goalposts have got to be moved farther down the field.'

'They're dug in,' he claimed.

A demonstrator is detained as activists rally inside the Senate Hart Office Building during a protest in opposition Kavanugh on Thursday

Protesters hold up signs during a protest against Kavanaugh outside the Supreme Court on Thursday

Massive presence: This was the scene in the courtyard of the Hart Office Building, one of the areas where senators have their offices on Capitol Hill

Judiciary Committee Chairman Chuck Grassley scolded the press, saying that when reporters came to his office to interview protesters, they only sought to speak to activists who opposed Kavanaugh.

'That's a bias that none of you should be proud of!' the normally calm Iowan boomed.

Protesters swamped the Capitol again on Thursday, holding anti-Kavanaugh demonstrations inside and outside U.S. Senate buildings - 302 people were arrested.

Some Republican senators have expressed unease over protesters who have confronted them inside their offices, restaurants, airports and even outside their homes. They discussed security matters behind closed doors earlier this week at a private lunch.

United States Capitol Police have arrested dozens of protesters in recent days and stepped up their presence in Capitol hallways.

The impassioned fight over Kavanaugh's nomination has also led to heightened security at the Capitol, with some senators using police escorts to shield them from protesters.