Majority Leader Mitch McConnell (R-Ky.) said on the Senate floor that “the Democratic Party held out hope that the legal system would undo their loss in 2016. They refused to make peace with the American people’s choice.” (Alex Brandon/AP)

Republicans on Tuesday rallied behind President Trump’s effort to quash lingering questions raised by special counsel Robert S. Mueller III’s report on Russian interference in the 2016 election.

Senate Majority Leader Mitch McConnell (R-Ky.) declared “case closed,” insisting that Democrats should accept Mueller’s findings and end their investigations. Almost simultaneously Tuesday morning, the White House invoked executive privilege to block former counsel Donald McGahn from complying with a congressional subpoena for documents.

McConnell’s comments represent a new front in the GOP resistance campaign, bolstering a weeks-long effort by the Trump administration to stonewall multiple oversight demands from House Democrats ahead of the 2020 election. Attorney General William P. Barr released a redacted, 448-page version of the Mueller report April 18, and Republicans say it is time to move on.

“For two years, the Democratic Party held out hope that the legal system would undo their loss in 2016. They refused to make peace with the American people’s choice. But the American people elected this president,” McConnell said in a speech on the Senate floor, echoing Trump’s blasts at critics who he says are questioning his legitimacy.

The political broadside stood in stark contrast to a legal assessment from more than 700 former prosecutors from Republican and Democratic administrations, who signed a letter asserting that Trump would have been charged with obstruction of justice based on Mueller’s findings were he not president.

The signers included some left-leaning lawyers who have become household names for their frequent TV appearances, but also several career prosecutors and high-profile conservatives who thought Barr had so mischaracterized Mueller’s report that they needed to set the record straight.

Paul Rosenzweig, who served as senior counsel to independent counsel Kenneth W. Starr, said he signed the letter to present a counterpoint to what he called Barr’s “erroneous” assertion that the evidence was insufficient to accuse Trump of obstructing justice.

He also had a personal reason: When Starr investigated President Bill Clinton in the late 1990s, Clinton’s defenders raised similar arguments — and successfully avoided his removal from office.

“I lost that fight, but I will stand to the end of my days that presidents should not lie under oath and should not suborn perjury from others — period, full stop,” said Rosenzweig, a member of the conservative Federalist Society. “I realize that’s a low bar, but apparently it’s not low enough for the American public.”

The letter, first publicized Monday, had gained more than 730 signatures by Tuesday evening.

Inside the Capitol, Republicans stood with Trump, as they have repeatedly since the start of his presidency. Sen. Rand Paul (R-Ky.), who frequently talks about the Constitution, said he was not concerned about the precedent the White House was setting in ignoring congressional subpoenas. He said he was more worried about the Democratic effort to obtain Trump’s tax returns, likening it to a Pandora’s box that would create a “system where each party goes after the donors and the political parties and the candidates.”

“The biggest problem right now is the idea that we can destroy the whole concept of your taxes being private,” he said. “It’s an awful precedent. I think the Democrats ought to think twice before they open this door.” 

GOP Sens. Susan Collins (Maine) and Cory Gardner (Colo.), both seeking reelection next year in states Trump lost in 2016, declined to challenge McConnell’s view, with Gardner using Trump’s oft-repeated assessment.

“The report talks about no collusion, no cooperation, so what are you talking about?” Gardner said, referring to Democrats’ accusations of malfeasance. “Look, we have work to do to make sure Russia doesn’t continue to try to influence the elections. I think that’s a major concern that we have — I think that’s what I want to continue to focus on.”

Collins said Mueller’s testimony “would be helpful” to “get clarifications on some of the issues.” But key GOP lawmakers, including Senate Judiciary Committee Chairman Lindsey O. Graham (S.C.) and Intelligence Committee Chairman Richard Burr (N.C.), are not currently seeking his testimony.

“I take his report as an encapsulation of the very narrow area he was looking at: potential of criminal acts and his conclusions. I take for granted Bob Mueller put in his report exactly what he found and exactly what he wanted the American people to read,” Burr said Tuesday.

On the other side of the Capitol, House Republicans who doggedly investigated President Barack Obama’s IRS and his administration’s handling of the deadly 2012 terrorist attacks on U.S. facilities in Benghazi, Libya, shrugged — and turned their fire on Democrats. 

“Frankly, Democrats are choosing conflict when compromise is available to them,” said Rep. Mark Meadows (R-N.C.), a member of the House Oversight Committee who is close to Trump. “The way the Democrats are issuing subpoenas . . . is fundamentally different and more aggressive than it was when a Republican majority was in the House and Obama was in the White House.”

The GOP response came as the White House invoked executive privilege to bar McGahn from giving the House Judiciary Committee documents related to Mueller’s probe. The White House argued that McGahn — who was a central witness to Mueller’s investigation of whether Trump obstructed justice — did not have the authority to share the material.

Democrats countered that the White House waived privilege the moment it allowed McGahn to cooperate with Mueller’s investigation — and again when Mueller made McGahn’s testimony public in his final report. The Judiciary Committee threatened Tuesday night to hold McGahn in contempt of Congress along with Barr, who is expected to be held in contempt Wednesday morning for refusing to hand over the unredacted Mueller report.

“I fully expect that the committee will hold Mr. McGahn in contempt if he fails to appear before the committee, unless the White House secures a court order directing otherwise,” said panel Chairman Jerrold Nadler (D-N.Y.).

Democrats on Tuesday assailed McConnell and Republicans for seeking to move past Mueller’s findings. The House Judiciary Committee is trying to secure Mueller’s public testimony as soon as this month, but Trump is openly opposing further testimony while touting Mueller’s report as vindication. It is unclear when, or whether, the dispute might be settled. 

Senate Minority Leader Charles E. Schumer (D-N.Y.) called McConnell’s speech “an astounding bit of whitewashing — not unexpected but entirely unconvincing.”

“It’s sort of like Richard Nixon saying, ‘Let’s move on’ at the height of the investigation of his wrongdoing,” Schumer said. “Of course he wants to move on. He wants to cover up. He wants to silence.”

That was only one of multiple invocations of former president Richard M. Nixon, who resigned in 1974 shortly before an imminent House impeachment vote. With Trump and his administration refusing to comply with congressional requests, Democrats weighed various options, from launching an impeachment probe to holding officials in contempt of Congress to a growing list of legal challenges.

But with clear reservations among the party leadership about impeachment proceedings, Democrats have struggled to chip away at the Republican wall of resistance. Increasingly, they are realizing that they must look to the courts to save their oversight authority, a process that could take years as they challenge each attempt by the Trump administration to bar Congress from requesting witnesses and documents.

House Speaker Nancy Pelosi (D-Calif.), speaking Tuesday at a New York event hosted by Cornell University, captured her party’s dilemma. Trump, she said, “is goading us to impeach him.”

“Because he knows it would be very divisive in the country, but he really doesn’t care — he just wants to solidify his base,” she said. “We can’t impeach him for political reasons, and we can’t not impeach him for political reasons. We have to see where the facts take us.” 

On a day when a Democratic presidential candidate, Sen. Elizabeth Warren (Mass.), called for impeachment on the Senate floor, Schumer also stopped short: “We should have hearings. We should thoroughly investigate the Mueller report. We ought to seek every aspect of the Mueller report. And then we can make a decision.”

But McConnell made it clear that even if House Democrats impeached Trump, there would be no GOP votes in the Senate to convict and oust the president.

The Republican leader, in the final months before the 2016 election, repeatedly undermined efforts by the Obama administration to warn the public about Russian interference and send a bipartisan message to Moscow.

When then-CIA Director John Brennan met privately with McConnell in late summer 2016 to brief him on alarming new intelligence about Russia’s plans to derail the race, McConnell cast doubt on the underlying intelligence and threatened to accuse the White House of political meddling if it brought the issue to the public’s attention.

“You’re trying to screw the Republican candidate,” McConnell said, according to officials familiar with the exchange. The response startled Brennan and others, who thought the intelligence — including details about Russia’s hack of the Democratic National Committee and Russian President Vladi­mir Putin’s involvement in the operation — was so overwhelming that Republicans would rally around plans to confront Moscow.

McConnell is seeking reelection next year, and his campaign Tuesday sent out a fundraising solicitation boasting that he had “just told the Democrats to end their Russia conspiracy spectacle and accept there was no collusion. CASE CLOSED.”

“It’s time to move on,” McConnell told reporters. “There was no collusion.”

Josh Dawsey, Karoun Demirjian, Carol D. Leonnig and Greg Miller contributed to this report.