Around the time of Donald Trump’s inauguration, Ben Wikler began visiting the DC offices of Senate Democrats to press them to fight harder against the new president. The director of the progressive group MoveOn.org, Wikler wanted to know if they would do everything they could to block the Republican agenda.

He got a lukewarm reception. “They were really nervous about objecting to routine and procedure because it might disrupt the comity of the body,” Wikler said. “It was on everyone's mind: What would be the cost to the institution they love?”

Almost since its founding, the US Senate has run on an informal compromise between the minority and majority parties: “It was, ‘I won't use all my powers against you, and you in turn won’t use all of your powers against me,’” says former US Sen. Fred Harris (R-OK).

That arrangement, already under severe strain through decades of political polarization, is approaching a breaking point under the new administration, according to interviews with six current and former senators, as well as multiple congressional scholars and Hill staffers.

In the four weeks since Trump took office, Senate Democrats have taken unprecedented steps to oppose the Republican agenda. And the GOP has responded by rewriting the Senate rules, accelerating the transformation of the Senate into a body much more governed by strict partisanship.

“The old myth of the Senate is being blown up,” says Julian E. Zelizer, a historian of the US Senate at Princeton University. “It’s now a very partisan body. That’s the new Senate."

The US Senate was designed as a nonpartisan, deliberative body

The US Senate was designed to insulate its members from political pressures — to give it space to deliberate what’s best for the country removed from the public’s popular will.

Its members are appointed to six-year terms (as opposed to two years in the House). There are fewer members, elevating the relative importance of each.

“The Senate was meant to be less populist and less partisan,” Zelizer says. “It was supposed to be more cerebral, upper-class, and independent from the temper of the electorate, which the House was supposed to reflect.”

Over time, that founding ideal was translated into a set of rules that prized consensus among senators and made dissent paralyzing to its functioning.

Senators were forbidden from launching personal attacks “impugning” the character of their colleagues. Each senator had the authority to grind the body to a halt through the filibuster. The Senate’s legislative calendar is governed by what are called “unanimous consent” agreements, which allow any one senator to prevent bills from moving forward.

Those rules created a body that fostered personal bonds between senators as essential to lawmaking. “The Senate used to be a place where you’d get to know each other — they’d travel together, they’d attend lectures together, they’d hang out before and after session,” says Jane Calderwood, a Hill veteran of 20 years who served as chief of staff for former Sen. Olympia Snowe (R-ME). “All of that became crucial to legislating. At least it used to be.”

Democrats have accelerated a “clamping down” on minority rights in the Senate

Now, the ideal of the “collegial” Senate has always been something of a historic myth. All you have to do is look at the witch hunts of Sen. Joseph McCarthy (R-WI) to know the body hasn’t always dispassionately considered solutions far from the partisan fray.

But that notion has been particularly difficult to sustain over the past 30 years. As political polarization began pulling the parties apart, the Senate has more and more resembled the House of Representatives — with the parties’ leaders exerting increasing control of the legislative agenda, and new restrictions that limit the time for debate on the Senate floor, according to Zelizer, the Princeton historian.

“There’s this process of spiraling animosity: The minority abuses its privileges of endless debate, and then the majority retaliates by clamping down,” says Josh Huder, a congressional scholar at Georgetown. “The Senate was built around consensus lawmaking, and so it’s really straining under this new political reality.”

As the space for compromise between the parties shrank, the willingness of the majority to put up with dissent from the minority went with it. That story is being replayed in the new administration:

Senate Democrats have cast an unprecedented number of votes against Trump’s Cabinet nominees, creating the slowest confirmation process in modern US history.

Senate Democrats have boycotted the committee hearings of three Trump Cabinet nominees. That led Republican committee chairs to rewrite the rules of their confirmation processes, so they no longer required quorums to send Cabinet nominees to the floor.

Sen. Elizabeth Warren (D-MA) violated Rule 19 of the Senate code prohibiting members from openly impugning the character of another senator, Attorney General Jeff Sessions. Senate Majority Leader Mitch McConnell (R-KY) retaliated by censuring Warren on the floor — something that’s been done only a handful of times in American history. (His decision to silence Warren was upheld in a strict party-line vote.)

Democratic senators are now openly considering filibustering Trump’s Supreme Court nominee, partly in retaliation against Republicans’ refusal to schedule a hearing for Merrick Garland, President Obama’s nominee. If Democrats do so, Republicans might change the filibuster rules to only require 51 votes, rather than 60, for Supreme Court confirmation.

All of this reflects the pressure Senate Democrats are under from their base to use whatever tools are at their disposal to fight Trump. “It was really scary for Democrats to risk being willing to go beyond the normal operations,” says Wikler, of MoveOn.org. “That fear is being overcome by a recognition that these are not normal times.”

“A degradation of the tools themselves”

To some, the rise in tactics that have increased Senate partisanship is itself a bad thing. Senators are wedded to the idea that they belong to “the world’s greatest deliberative body” — whether they’re in power or not — and openly fret that what’s being lost is something more important than party politics.

“It’s been very troubling. I’m very worried about it,” Sen. Jeff Flake (R-AZ) said in an interview.

Similarly, Sen. John Hoeven (R-ND) also worries friendships across the aisle are under threat: “Right now, it’s certainly challenging. I hope it’s Democrats still trying to adjust to the new administration.”

In a floor speech on Thursday highlighted by the Washington Post’s Chris Cillizza, Sen. Marco Rubio (R-FL) responded to Warren’s speech by lamenting the decay of Senate tradition of bipartisan collaboration. “We are reaching a point in this republic where we are not going to be able to solve the simplest of issues because everyone is putting themselves in a corner where everyone hates everybody,” Rubio said.

Publicly, Democrats refuse to say that what’s happened under Trump risks hurting the Senate.

“We’ve had a bad patch the last few days, but the Senate is a very strong institution and ultimately a very collegial institution,” says Sen. Richard Blumenthal (D-CT).

But in private, even those who think the party is doing the right thing also worry about its impact on the institution as a whole. “We’re using the tools of the institution to deal with an extraordinary circumstance, even though doing so will lead to a degradation of the tools themselves,” said one senior Democratic Senate aide.

The aide added: “There’s an obligation some here feel, or have felt over time, to read the Constitution and decide that civility and comity and all of those high-minded, old-fashioned words really matter — that there’s an important muscle memory to this place that’s worth preserving. But that’s clashing with all of us wanting to win and defeat this guy that that most of us regard as an abomination.”

“We get way too fussy over ‘the perceived order of things’”

But if some members of both parties worry that something valuable is being lost in the new partisan environment, others argue that nostalgia for the comity of the old Senate is both misguided and potentially dangerous.

Sen. Brian Schatz (D-HI) says he’s enjoyed playing basketball with Sen. Ted Cruz (R-TX), and had fun going to dinner with Sen. Pat Toomey (R-PA). But he dismisses out of hand the idea that the Senate tradition of bipartisan friendships are themselves essential to lawmaking.

“I think there is an old saw in Washington — and it’s mostly among the chattering class that used to love their cocktail parties — that the problem is a lack of personal relationships,” Schatz says. “What a luxury to be in this gilded place, this literally gilded place, and worry about decorum.”

Some frame the debate as an almost existential question for the Democratic Senate caucus: Does the Senate make sure it does everything it can to stop the worst abuses of Trump? Or will hesitancy over ending friendships across the aisle limit the ferocity of the resistance?

There’s no doubt about where Schatz comes down. “People are conflating the violation of social norms with the violation of rules and laws ... We get way too fussy over the ‘perceived natural order of things’ and ‘institutional prerogatives,’” he says. “All of that stuff has to go over time. But what should be unbreakable is our commitment to constitutional government.”

In 2013, Sen. Harry Reid (D-NV) used the “nuclear option” so Democrats only needed 51 votes, rather than 60, to confirm Cabinet nominees. That change could be extended not just to the Supreme Court but also to much more routine legislative procedure, like passing a budget.

Doing so would strip the Senate minority of some of its rights to object to certain legislation. And it would further erode the need for the parties to work together to get anything done.

But that itself may come with an unexpected upside. If the Senate does away with the rules requiring unanimity and supermajorities, it would make the body much more democratic — and more responsive to the country overall — because it would reduce the barriers for the majority of the country to implement its agenda once in power.

That’s something liberals have long wanted out of the American political system — even if they get it because of changes that are helping the Republican Party push through a platform they oppose.

“Having an anti-majoritarian Senate is a relic of the founding of the country — why shouldn’t we have simple majority rule?” Zelizer says in explaining liberals’ perspective on the Senate’s limitations. “If the outcome of this is to blow up the filibuster altogether, Democrats will in the long run will have an institution that's more capable of making decisions. Even if it’s more partisan.”

Correction: A previous version of this story incorrectly suggested Sen. Brian Schatz (D-Hawaii) was open to “shredding Senate norms.” In fact, he was speaking of the limits of bipartisan Senate friendships to achieve legislation.

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