Senate Democrats who are angry at Republicans for refusing to confirm President Barack Obama's final Supreme Court nominee are threatening revenge and plotting to throw up roadblocks to stymie President-elect Donald Trump's cabinet picks.

Senior GOP senators have refused to schedule Merrick Garland for a vote since his mid-March nomination to fill the seat of deceased justice Antonin Scalia.

'Past is present, and what goes around comes around,' California Sen. Dianne Feinstein told Politico on Monday.

'Now, those are pretty hackneyed sayings, but those are really true around here.'

'What comes around goes around' Democratic Sen. Dianne Feinstein said Democrats will play the tit-for-tat game by slowing down Trump cabinet confirmations as payback for stonewalling on President Obama's final Supreme Court nominee

Trump will rely on Sen. Mitch McConnell (right), the majority leader, to push his nominees through a bickering, partisan Senate

Feinstein will retire when the new Senate is sworn in, but others said they will delay the confirmation of the incoming White House's top men and women.

Because of a rule change that Minority Leader Harry Reid pushed through when he was the majority leader three years ago – the so-called 'nuclear option' – the GOP will only need a simply majority of 51 votes to confirm cabinet secretaries.

The rule had previously required a supermajority of 60. Republicans will take full advantage, leaving Democrats only with delaying tactics in their arsenal.

But some liberal senators say they'll play every card they have, including drawing out the process as long as possible.

'They've been rewarded for stealing a Supreme Court justice. We're going to help them confirm their nominees, many of whom are disqualified?' Ohio Democratic Sen. Sherrod Brown complained to Politico.

'It's not obstruction, it's not partisan, it's just a duty to find out what they'd do in these jobs.'

Democrats could also force each nomination to consume as many as 30 hours of debate, tying up the ambitious but time-starved Senate

In 2009 the Republican minority put up a fight over just one nominee – Secretary of State Hillary Clinton, allowing Democrats to clear more than a dozen senior nominees in the first week without a fight.

Even in Clinton's case, they merely demanded a roll-call vote, a minor calendar-shift.

Billionaire Steve Mnuchin, Trump's pick to be secretary of the treasury, could receive a Democratic grilling over his ties to Wall Street

Sen. Jeff Sessions could be put through the wringer by Democratic senators who insist they see him as a throwback to southern racism and don't want him to be attorney general

It's not hard to read between the lines of what Democrats are promising this time around.

'I don't want to needlessly prevent President Trump from being successful,' Delaware Sen. Chris Coons said. 'But accelerating the confirmation of unacceptable candidates who have views that are outside the mainstream is not constructive.'

Don Stewart, a spokesman for Majority Leader Mitch McConnell, told Politico that a 'smooth transition' is 'something President Obama recently called for and that Democrats always say they want.'

'When the shoe was on the other foot, Republicans worked with Democrats to confirm the president's Cabinet in a very, very timely manner.'

But Connecticut Democratic Sen. Richard Blumenthal said senators should demand roll-call votes 'on every one of the president's Cabinet nominees.'

That would give Democrats the option of abstaining – even as a group – in order to paint Trump's cabinet confirmations as products of unilateral partisan voting.

U.S. Court of Appeals Judge Merrick Garland's Supreme Court nomination has languished in purgatory for nearly 9 months because Republicans insisted that the incoming president should choose the late Justice Antonin Scalia's replacement

Ohio Democratic Sen. Sherrod Brown has revenge on his mind: 'They've been rewarded for stealing a Supreme Court justice. We're going to help them confirm their nominees?'

They could put up an even bigger fight on Defense secretary-designate Gen. James Mattis. Since he hasn't been a civilian for the required seven years, he will need a waiver from Congress in order to run the Pentagon.

That vote requires a 60-vote supermajority in the Senate.

At least one Democrat says the threats of delaying tactics by his own party on attorney general-designate Jeff Sessions are 'just bull***t.'

'My God, I think we should have an attorney general in place on Jan. 20. I sure do believe that,' West Virginia Sen. Joe Manchin said.

Manchin will run for re-election in 2018 in a deep-red state.

He's also in line for a possible Trump cabinet appointment himself.

Democratic Sen. Joe Manchin of West Virginia (left) and Republican Sen. Ted Cruz of Texas (right) are both expecting the Senate to push through fast confirmations – and they could both be nominees themselves

The two senators from Texas, both Republicans, said last month that they were confident Trump's cabinet will ultimately be confirmed.

'We're going to confirm the president's nominee one way or the other. And there's an easy way and there's a hard way,' Sen John Cornyn, the majority whip, said.

'They just need to accept that reality.'

Sen. Ted Cruz predicted that 'the Democrats will not succeed in filibustering a Supreme Court nominee. 'We are going to confirm President Trump's conservative Supreme Court justices.'

Cruz, like Manchin, could be the nominee who tests that confidence.