When John Thune, Republican of South Dakota, stood on the Senate floor in January for the first time as the majority leader, he promised he would maintain the chamber’s norms and traditions, keeping alive a healthy spirit of debate and adhering to longstanding, though increasingly embattled, precedents.
“One of my priorities as leader will be to ensure that the Senate stays the Senate,” Mr. Thune said. “That means preserving the legislative filibuster, the Senate rule that today perhaps has the greatest impact on preserving the founders’ vision of the United States Senate.”
More than eight months into his tenure, the filibuster remains in the Senate’s tool kit. But Mr. Thune, like leaders of both parties before him, has presided over a substantial dulling of its edge.
On Wednesday, Republicans, led by Mr. Thune, completed a rare maneuver that effectively changed the Senate’s rules to allow blocs of nominees to be confirmed by a simple majority vote rather than a 60-vote supermajority, a move they muscled through along party lines. Mr. Thune called it a necessary corrective to end a Democratic blockade that was stalling confirmation of President Trump’s appointees.
But the move marked the third time this year that Mr. Thune had steered around Senate precedents to advance Mr. Trump’s priorities. In the process, he has strayed from his reputation as an institutionalist and bowed to the rough-and-tumble politics of an increasingly polarized Congress.
In May, Mr. Thune made an end run around the filibuster to block California’s plan to phase out gas-powered vehicles, turning to a complicated procedural process to help ease some Republicans' concerns over unilaterally rewriting Senate rules.
The next month, on a party-line vote, Republicans set a new precedent that upended how the costs of tax cuts are counted in federal budgeting, moving to lock in an accounting gimmick that smoothed the path for enactment of Mr. Trump’s sprawling domestic policy bill. The change eroded one of the last bulwarks against unchecked deficits and dealt a blow to the filibuster, vastly expanding the scope of fiscal policy bills that can be pushed through on a simple majority vote.
The latest change on nominees effectively eliminated senators’ power to slow the consideration of individual nominees, by insisting they be subject to further scrutiny or a separate formal vote. The move undercut the chamber’s constitutional role of vetting the president’s selections.
Taken together, the changes, all approved on simple-majority votes, have chipped away at the strength of the filibuster, once a powerful Senate tool that could be used to protect the rights of the minority party by encouraging senators to find consensus.
Mr. Thune has maintained that the change advanced this month was intended not to eviscerate a Senate tradition but to return the chamber to the efficient, working order of the past that he promised to uphold in his January speech.
Strictly speaking, he has adhered to his vow. Despite this month’s change speeding the consideration of groups of presidential nominees, Mr. Thune has not sought to eliminate the 60-vote threshold for advancing major legislation. In contrast, when Democrats were in the majority, they actively explored chipping away at the filibuster for voting rights legislation, but lacked the votes in their own ranks to do so.
The power of the legislative filibuster remains alive and well, for instance, as a Sept. 30 deadline to fund the government approaches. Senate Republicans lack the votes to pass a stopgap measure without support from Democrats, who are demanding health care concessions in exchange.
Still, congressional experts said that Mr. Thune’s piecemeal changes have dealt a significant blow to the minority party’s ability to force bipartisan consensus, which was once a foundational goal of the Senate but in recent decades has faded with the rise of a more tribal politics.
Eric Schickler, a professor at the University of California, Berkeley, said that Mr. Thune’s maneuvers reflected some concern about Senate precedent. He pointed out that Mr. Thune had avoided directly overruling the Senate parliamentarian, who enforces the chamber’s rules and precedents.
But Mr. Schickler said that the recent change on nominations suggested that Mr. Thune was more flexible in some regards than his remarks in January indicated.
“If the filibuster gets in the way in a serious way of something that Republicans are otherwise unified on, he’s going to find a way around the filibuster,” he said of Mr. Thune.
Several Republican senators who are thought of as institutionalists supported Mr. Thune’s change this week, dismissing concerns about the fate of the filibuster. Instead, they cast the maneuver as a necessary response to a unified Democratic effort to stall all of Mr. Trump’s lower-level nominees on principle, something Republicans portrayed as a threat to a body that has long prided itself on collegiality.
“I don’t think it weakens the filibuster at all,” Senator Susan Collins of Maine said. “I think it’s an unfortunate situation that we are in. But not a single nominee of the Trump administration has been confirmed by voice vote.”
Many presidential picks below the cabinet level have traditionally been confirmed through voice votes or by unanimous consent, essentially an agreement by all senators to bypass time-consuming debate. But Democrats have demanded that every position be subject to individual consideration, eating up floor time and slowing the Senate’s already deliberative pace.
Mr. Thune, who has served in the Senate since 2005, cited these delays as justification for changing the rules, arguing that Democrats’ obstruction was the real threat to the institution.
In that sense, he is just the latest in a long line of Senate leaders of both parties who claimed they had been forced to overhaul the institution’s norms in the face of an incendiary political environment that they blamed on their opponents.
Democrats took the first bite out of the filibuster in 2013, when they confronted a Republican effort to block judicial nominees. Senator Harry Reid of Nevada, then the majority leader, turned to a series of straight majority votes to lower the filibuster threshold to a simple majority on lower-court judicial nominees and most executive branch picks.
That maneuver was once thought to be so anathema to the spirit of the Senate that it was named the “nuclear option,” in part because of the devastating partisan fallout it would leave in its wake. Senators warned that the move would lead to mutually assured destruction: If the majority party unilaterally began chipping away at the filibuster, the minority party would retaliate when it took power, leaving wreckage across the political spectrum.
Senator Mitch McConnell, Republican of Kentucky, made a similar move in 2017, when he turned to the nuclear option to end a Democratic filibuster of Mr. Trump’s Supreme Court picks. He used it again in 2019 when Republicans went nuclear to speed up the confirmation of district court judges and executive branch nominees.
Richard A. Arenberg, who served as an aide to three Democratic senators and wrote a book in defense of the filibuster, said that each small change only cleared the way for the next one.
“We are on a bit of a slippery slope,” Mr. Arenberg said. “Each time you cross a line, you know, it becomes a little bit easier to cross the next one.”
And Republican senators have signaled that they would deploy their new precedent without reservation while working through a backlog of nominees that has infuriated Mr. Trump.
“Over 100 more nominees will be ready for confirmation by the end of this week, to get that process moving,” Senator John Barrasso of Wyoming, the No. 2 Republican, said on Wednesday. “It’s time for the Senate to clear the nominations backlog and clear it quickly. And so we will.”