Retiring Arizona Republican Sen. Jeff Flake on Wednesday vowed to pull support for all federal judicial nominees -- including 21 pending in the Judiciary Committee and 32 awaiting a vote on the Senate floor -- unless the Senate's GOP leadership permits consideration of legislation to expand protections for Special Counsel Robert Mueller's job.

The dramatic move by Flake, considered a potential primary challenger to President Trump in 2020, came immediately after Senate Majority Leader Mitch McConnell blocked his effort to introduce the bill for consideration by unanimous consent, which requires the approval of all 100 senators.

McConnell said the legislation, also backed by Delaware Democratic Sen. Chris Coons, is unnecessary because Trump has not suggested he will fire Mueller. (Other conservative commentators have suggested that the law would be unconstitutional, on the separation-of-powers theory that Congress does not have the authority to strip the president of the authority to fire Executive Branch officials he oversees.)

"Sen. Coons and I are prepared to make it again and again until there is a vote on this vital, bipartisan legislation on the Senate floor," Flake said in a speech just weeks before his imminent retirement. "And I have informed the majority leader I will not vote to advance any of the 21 judicial nominees pending in the Judiciary Committee or vote to confirm the 32 judges awaiting confirmation on the Senate Floor until S. 2644 is brought to the full Senate for a vote."

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He added: "We have been told that the bill ... is not necessary, as there have been no indications that the independence of Mr. Mueller's investigation is in jeopardy. That may have been an arguable position before last week. But it is not arguable anymore.

"With the firing of the attorney general ... the president now has this investigation in his sights and we all know it," he continued. "How such an investigation can be the cause of controversy is beyond me. ... Presidents do not get to determine what gets investigated and what and who does not."

"The President now has this investigation in his sights, and we all know it." — Sen. Jeff Flake, R-Ariz.

Wednesday's threat wasn't the first from Flake, who will be replaced in January by Democrat Kyrsten Sinema. In June, he told ABC News that he was considering using judicial nominees as leverage over trade policy. ("I think myself and a number of senators, at least a few of us, will stand up and say let's not move any more judges until we get a vote, for example, on tariffs," Flake said this summer.)

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Flake was a key vote to confirm Supreme Court Associate Justice Brett Kavanaugh, and he is the swing vote on the Judiciary Committee, where Republicans hold a slim 11-10 majority. The Senate, which has the exclusive power to confirm federal nominees by a simple majority vote, will be in session for another week in November and about two more weeks in December.

The pending judicial nominees do not need majority support on the Judiciary Committee to advance to a final confirmation vote on the Senate floor, where Republicans are set to retain their majority next term. However, nominations that do not have the committee's approval tend to move slower.

Judiciary Committee Press Secretary George Hartmann wrote on Twitter that the committee is planning to vote on a set of nominees soon.

"As for the nominees in committee on tomorrow's [Judiciary Committee] agenda, they are all expected to be held over one week under the committee rules (which do not require a vote)," Hartmann wrote. "They would, however, be ready for a committee vote at the following business meeting (likely Nov. 29)."

Top Democrats and some Republicans have called on Acting Attorney General Matthew Whitaker, who replaced Jeff Sessions, to recuse himself from oversight of the Russia investigation. Whitaker has written critically of Mueller's probe, which he now oversees.

The bill Flake advocated, which has been stalled in the Judiciary Committee since earlier this year, would have mandated an expedited judicial review of any decision by Trump to fire Mueller. If the termination was found to be without cause, the legislation would restore Mueller's job.

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Senate Minority Leader Chuck Schumer, D-N.Y., said this week that if Whitaker does not recuse himself, Democrats will seek to tie protections for the investigation into the critical spending bill that funds the federal government -- potentially setting up a government shutdown.

"We Democrats, House and Senate, will attempt to add to must-pass legislation, in this case the spending bill, legislation that would prevent Mr. Whitaker from interfering with the Mueller investigation" should Whitaker not recuse, Schumer said Sunday during an appearance on CNN's "State of the Union."

Under current Justice Department guidelines, Mueller's termination would ostensibly have to come from Whitaker or another high-level DOJ official.

But one of the bill's co-sponsors, North Carolina Republican Sen. Thom Thillis, sided with McConnell in saying that there's no rush to pass the bill.

"I don't think the president has any intention of removing Mueller," Thillis said. "I'm all about getting this on the books so no future President can make that kind of a bad decision. ... I've had discussion with the president. Everyone said it was hours away back in August. Didn't happen. So I think it's another false crisis. But it's important legislation ultimately to get passed."

Fox News' Jason Donner, Andrew O'Reilly, and Chad Pergram contributed to this report.