WASHINGTON >> The fight over the filibuster escalated in the Senate today as Sen. Mitch McConnell, the Republican leader, threatened harsh reprisals if Democrats moved to weaken it, a prospect that appeared increasingly likely as President Joe Biden’s allies on Capitol Hill began building a public case for its elimination.

After Sen. Richard Durbin of Illinois, the No. 2 Senate Democrat, called for changes to reduce the power of the procedural tactic, McConnell, R-Ky., bluntly promised a “scorched-earth” response and pledged to grind the Senate to a standstill and derail Biden’s agenda if Democrats took that step.

“Everything that Democratic Senates did to Presidents Bush and Trump, everything the Republican Senate did to President Obama, would be child’s play compared to the disaster that Democrats would create for their own priorities if — if — they break the Senate,” McConnell said.

McConnell was referring to the prospect that Democrats might resort to a move known as the “nuclear option,” using their majority status to force a change in the Senate rules that allow lawmakers to block action on a bill unless proponents can muster 60 votes to move forward. That would effectively destroy the filibuster, allowing the majority party — currently the Democrats — to muscle through any measure on its own.

Progressives have been agitating for such a change to allow Biden to steer his agenda around Republican obstruction, and a growing number of Democrats are openly considering it. The idea has gained strength after the enactment of Biden’s $1.9 trillion stimulus measure, which Democrats pushed through the Senate without a single Republican vote under a special budget process, delivering legislation that has so far been well received by the public and given Democrats a taste of the possibilities of a postfilibuster world.

Seeking to slow Democrats and get the attention of the White House, McConnell was adamant that Republicans would tie the Senate into knots in retaliation if they took the step. He issued his warning after Durbin, a respected veteran of the institution, had said on Monday that it was time to stop allowing the minority party to routinely block legislation by requiring a three-fifths majority to advance most bills. It was the most explicit call yet by a Democrat leader to take action.

Durbin noted that it was McConnell who institutionalized the use of the filibuster, which historically had been used rarely before the Kentuckian was in charge. Durbin said the procedural weapon was a particularly sore point for him, since it is has for two decades prevented Democrats from enacting the so-called DREAM Act, a popular bipartisan bill that he wrote that would create a path to legal status for unauthorized immigrants brought into the United States as children. Although it has majority support, it has never been able to clear the 60-vote threshold.

“I brought it to the Senate floor on five different occasions, and on five different occasions, it was stopped by the filibuster,” Durbin said Tuesday.

In his speech Monday, Durbin said the routine deployment of the filibuster had “turned the world’s most deliberative body into one of the world’s most ineffectual bodies” and argued the burden should be shifted to opponents of a given bill to maintain a filibuster rather than on supporters to produce 60 votes to advance it.

“No more phoning it in,” Durbin said. “If your principles are that important, stand up for them, speak your mind, hold the floor and show your resolve.”

Democrats say they are not yet ready to move ahead with any attempt to overhaul the filibuster rules and they also lack votes in their own party to do so at the moment. For now, activists are urging them to build momentum by following the same strategy that they employed in 2013 before they used the nuclear option to effectively do away with filibusters against executive and judicial branch nominees.

That year, Harry Reid of Nevada, then the Senate majority leader, lined up a series of three highly regarded judicial nominees for vacancies on a prestigious appeals court to show that Republicans were going to block Obama administration nominees no matter how qualified they were. Democrats then brought up the nominees repeatedly for floor votes and failed to break Republican filibusters, a process that eventually persuaded enough senators in their ranks that they had no choice but to lower the 60-vote threshold for nominees to prevent the Obama administration from being denied its right to seat judges.

Senators appear to be increasingly responsive to appeals to end the filibuster as it now exists as they look ahead to the possibility of months of Republican resistance to their agenda.

“I think people have just had it,” said Sen. Amy Klobuchar, D-Minn., who leads the Rules Committee, about the blocking tactic that she had endorsed in the past. “I don’t think we should let an antiquated Senate rule undermine the foundation of our democracy and stop us from making progress.”

Klobuchar intends to convene a hearing next week on the broad voting rights bill already passed by the House, and she acknowledged that it was likely to “be a major test of the filibuster.”

In his comments, McConnell threatened that Republicans would turn the rules against Democrats and try to make it virtually impossible to do anything in the Senate if they proceeded with the change. He referred to the fact that the chamber operates under arcane rules often bypassed through what is known as a unanimous consent agreement where no senator objects. If Democrats plunged ahead to gut the filibuster, he warned, Republicans would deny consent even on the most mundane of matters, effectively bogging down the Senate.

“Let me say this very clearly for all 99 of my colleagues,” McConnell said. “Nobody serving in this chamber can even begin — can even begin — to imagine what a completely scorched-earth Senate would look like — none. None of us have served one minute in a Senate that was completely drained of comity, and this is an institution that requires unanimous consent to turn the lights on before noon.”

McConnell, who noted that he had resisted aggressive demands by President Donald Trump to get rid of the filibuster and ram through Republicans’ agenda, said eliminating it would represent a transformative change in government and go far beyond what voters intended in electing Biden and the evenly divided Senate.

“Does anyone really believe the American people were voting for an entirely new system of government by electing Joe Biden to the White House and a 50-50 Senate?” he asked. “There was no mandate to completely transform America by the American people on Nov. 3.”

Klobuchar disagreed with that assessment, saying that Americans did vote for a new approach and that ditching the filibuster might be necessary to achieve it.

“They voted for someone who is more moderate for president but someone who is going to do big things,” she said. “They voted for change.”

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