Sen. Bill Cassidy has been signaling for a few months that he wants to be a more independent force. After the November elections, in which the Louisiana Republican easily won a second term, Cassidy joined a bipartisan group that broke a negotiating logjam and paved the way for a $900 billion pandemic relief bill.

And on Jan. 6, as rioters supporting President Donald Trump were still being ejected from the Capitol, Cassidy condemned the attack in strong terms and demanded that Trump order the mob to stand down. “He needs to speak, because the president can speak as no one else can to these folks,” Cassidy told a Louisiana TV station that day.

But few expected Cassidy’s next bold, independent step — breaking GOP ranks and voting to declare that Trump’s second impeachment trial is constitutional and should proceed — particularly after he initially voted to essentially dismiss the case.

Yet Tuesday evening, the gastroenterologist called the previous four hours of arguments about the case against Trump, charged with inciting the attack on the Capitol, as a clear instance of one side presenting an overwhelming argument while the other side lacked any clarity.

“Now I’m an impartial juror, and one side is doing a great job and the other side is doing a terrible job on the issue at hand, Cassidy told reporters after being the only senator to switch his position from the initial Jan. 26 procedural vote. “As an impartial juror, I’m going to vote for the side that did the good job.”

His reversal gave a short-term burst of momentum for the House Democrats presenting the case against the ex-president, but it also suggested that Cassidy is ready to take a more aggressive approach to being a bipartisan dealmaker, willing to break away from the powerful grip of Minority Leader Mitch McConnell (R-Ky.).

On Wednesday morning, during a background-only call, aides to the managers said Democrats held out hope that they can find other converts like Cassidy, believing that previously unseen security footage of the rampage to be presented Wednesday will be another jolt to senators.

Republicans, according to one Democratic aide, “are just now waking up from the grip of the former president.”

Other Republicans contend that 44 GOP senators have now voted twice to declare that the trial of an ex-president is unconstitutional, making it unlikely that a Republican would then switch his or her vote, unless some shocking new discovery emerges.

That means the votes are pretty well set in stone after Tuesday’s 56-to-44 roll call, still 11 votes shy of the two-thirds majority needed to convict Trump and move to the sentencing portion of the trial that would ban him from running for federal office again.

“I don’t think anyone expects it to be much different,” Sen. Marco Rubio (R-Fla.) said after Tuesday’s presentation. “I think we’ve had a lot of time to think over the last eight weeks about what happened, why it happened, why it shouldn’t have happened and, more importantly, what role the president played.”

If Rubio is right, that makes Cassidy’s vote all the more politically brave, for Trump will be acquitted and Cassidy will have angered Trump’s most fervent supporters, even if he eventually votes to acquit at the end of the trial.

“Very honest, very candid and very controversial among Louisiana Republicans,” Senate Majority Whip Richard J. Durbin (D-Ill.) said Wednesday, just before the day’s trial session began.

Indeed, one of Trump’s defenders, Rep. Mike Johnson (R-La.), lashed out at his home-state senator minutes after Tuesday’s vote, suggesting it will not sit well in a state that Trump won by about 19 percentage points in November.

“I was surprised by that,” Johnson told reporters. “I have not spoken to him, but I can tell you a lot of people from back home are calling me about it right now.”

The Louisiana Republican Party on Tuesday rebuked Cassidy for his vote.

Cassidy, 63, became a liver specialist after graduating from the Louisiana State University School of Medicine, eventually opening a community health clinic to help the uninsured in the Baton Rouge area. He won a House seat in 2008, and in 2014 Cassidy defeated a veteran Democratic Senate incumbent as part of a GOP wave.

Now, with a new six-year lease on his political life, Cassidy is starting to resemble a Republican version of John Breaux, a Louisiana Democrat who served three terms in the Senate and frequently angered both parties with his bipartisan dealmaking.

Breaux, who retired in 2004, represents a bygone era when Senate leaders were much less powerful than in the past decade, during which McConnell and his Democratic predecessor, Sen. Harry M. Reid of Nevada, consolidated power in the majority leader’s office.

After helping force the December pandemic deal, Cassidy now sees an opportunity for the power dynamics to shift.

“We don’t necessarily have to wait for something to come down from on high but can actually negotiate among ourselves and bridge differences that others would prefer to be unbridgeable,” Cassidy told reporters last week. He called it “very bracing” to rank-and-file senators to help push the $900 billion deal toward the finish line.

“So there’s a feeling that this is the way that we should operate,” he said. “It’s not been the way the Senate has operated, but it should operate that way.”

Last week he joined nine other Republicans at the first White House meeting President Biden convened with members of Congress, telling reporters afterward that the new president was “very gracious” to the GOP group.

The centrist Republicans appear to have lost in this initial round of negotiations — Biden has sided with Senate Majority Leader Charles E. Schumer (D-N.Y.) and House Speaker Nancy Pelosi (D-Calif.) to push through, solely with Democratic votes, a $1.9 trillion pandemic relief package.

Cassidy compared the breakdown in bipartisanship to marriage when reporters asked about the go-it-alone approach by Democrats. “Obviously the essence of any relationship is talking,” he said last week.

In the next few days, Cassidy must decide what his prescription is for Trump’s behavior. He said that while sitting next to Sen. Ted Cruz (R-Tex.) on Tuesday, he took notes and asked whether Trump’s attorneys were as bad as he thought.

They were.

So no one should be that surprised by his vote, he said. “It speaks for itself.”

More and more, Cassidy is doing just that, speaking for himself.