WASHINGTON (AP) — The Senate Judiciary Committee has canceled a Thursday vote on more than 20 federal judge nominations amid a standoff between Republican Sen. Jeff Flake and GOP leaders over legislation to protect special counsel Robert Mueller.

The Arizona senator, who is retiring from Congress, is a frequent critic of President Donald Trump. Flake has said he won't vote for any federal judges until Senate Majority Leader Mitch McConnell holds a Senate floor vote on the special counsel bill. The Judiciary panel, with an 11-10 Republican majority, doesn't have enough votes to advance nominees without Flake's support.

Confirming more judges before the end of the year is a top priority for McConnell, but he hasn't budged in his opposition to the special counsel bill, which he says is unnecessary.

On Tuesday, Texas Sen. John Cornyn, the No. 2 Republican in the Senate, said Republicans were counting how many votes they had on the special counsel bill — often a sign that legislation will be voted on soon. But McConnell said hours later that the bill is a "solution in search of a problem" because Trump is not going to act against Mueller.

"We have a lot of things to do, to try to finish up this year without taking votes on things that are completely irrelevant to outcomes," McConnell said.

Flake made his pledge after Trump pushed out Attorney General Jeff Sessions earlier this month and temporarily replaced him with a loyalist, Matt Whitaker, who has criticized Mueller's Russia investigation. Mueller is investigating Russian interference in the 2016 presidential election and Russian ties to Trump's Republican campaign.

Flake and Democratic Sen. Chris Coons of Delaware have repeatedly gone to the Senate floor and requested a vote on the legislation, which would give any special counsel a 10-day window to seek expedited judicial review of a firing. They did so again Wednesday, but Republican Sen. Mike Lee objected, arguing that the bill would undermine the separation of powers.

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In calling for the vote, Flake noted Trump's ongoing tweets criticizing Mueller and calling the probe a witch hunt. This week, Trump tweeted that Mueller is "doing TREMENDOUS damage to our Criminal Justice System, where he is only looking at one side and not the other."

Flake said that considering Trump's tweets on Mueller, "to be so sanguine about the chances of him being fired is folly for us, I believe."

Whitaker is now overseeing the Russia probe, taking over from Deputy Attorney General Rod Rosenstein. Rosenstein told Congress he saw no reason to fire Mueller.

Sessions, who worked on Trump's campaign, had recused himself from overseeing Mueller— a decision that infuriated Trump and led to Sessions' resignation.

Despite some GOP support, it is not clear that the special counsel measure could gain 60 votes in the Senate, and even less clear that Trump would sign a bill that contained the legislation. Democrats have said they will push for it to be added to a year-end spending bill.