The veteran senator is running for president, but he can’t talk about it. If he does -- if Bernie Sanders so much as whispers to a colleague on the Senate floor -- he can be hauled to prison for breaking with decorum.

Well, at least in theory.

The impeachment trial of President Donald J. Trump began on Tuesday with the sergeant at arms declaring “Hear ye! Hear ye! Hear ye! All persons are commanded to keep silent, on pain of imprisonment.” No senator has ever faced that consequence, making it mostly a ceremonial threat.

Undeniably more dangerous to Sanders’s White House aspirations are political attacks. Rivals past and present have taken advantage of the Sanders silence to bloody the presidential candidate-turned-mute impeachment juror.

Hillary Clinton’s voice re-emerged, however, just as the third impeachment trial in American history began. The former Democratic nominee told the Hollywood Reporter in a piece Tuesday morning that her former rival led a movement hostile to women. She declined to endorse Sanders publicly, but rather took the opportunity to tear into him personally.

“Nobody likes him,” Clinton claimed. “Nobody wants to work with him,” the former secretary of state complained of her old colleague. “He got nothing done,” she said before adding that Sanders “was a career politician” and that his appeal “is all just baloney and I feel so bad that people got sucked into it.”

The broadside once might have been a kiss of death for a Democratic candidate. But Clinton no longer reigns as party kingmaker, if she ever did, and Sanders apparently opted to turn the other cheek anyway.

“My focus today is on a monumental moment in American history: the impeachment trial of Donald Trump,” Sanders wrote in a statement. “Together, we are going to go forward and defeat the most dangerous president in American history.”

He certainly could have renewed hostilities with his old rival. Runner-up in the last primary, he might have noted how he threw his support behind Clinton. It also would have been within bounds to mention how he returned to the trail long after he lost the nomination to live out of a suitcase and campaign for her.

But Sanders set aside any curmudgeonly impulses and embraced self-deprecation. “On a good day, my wife likes me,” he quipped to reporters. “So, let’s clear the air on that one.”

Reporters later spotted Sanders on the Senate floor struggling to open what looked like a box of mints. He couldn’t quite remove the shrink wrap at first, and then he used his keys to cut through the plastic. The senator from Vermont later blew his nose. Little else was heard from Sanders otherwise for the better part of the 13-hour trial.

Some observers still note that Sanders was less forceful with Clinton than Massachusetts Sen. Elizabeth Warren. He accused Warren of lying about allegedly telling her a woman could not win the presidency. Meanwhile, some complain, he seemed to turn the other cheek with Clinton.

“It is not smart to re-litigate the 2016 debacle,” said Neil Sroka, communications director for Democracy for America. There wouldn’t be anything to gain, he told RealClearPolitics. Sanders now competes nationally for frontrunner status, Sroka argued, before emphasizing that “Bernie Sanders doesn’t need to trampoline off Hillary Clinton.”

Others saw a double standard in Sanders’s different approaches to criticism. “It is a bit frustrating that Sanders actively undercuts iconic progressive women like Elizabeth Warren but then pulls punches on the establishment with Joe Biden and Hillary Clinton,” a prominent progressive strategist said, speaking on condition of anonymity.

Many progressives are haunted by an old fear, one born from experience. They see Sanders and Warren trading blows in 2020 and remember the bad blood between former Missouri Rep. Dick Gephardt and former Vermont Gov. Howard Dean in 2004. Those Democrats also competed for the nomination in a familial battle that turned ugly. Meanwhile, then-Massachusetts Sen. John Kerry, an establishment favorite, was allowed to skate to the nomination.

As hostilities with Warren simmered, Sanders – whose campaign did not respond to RCP’s request for comment -- fanned similar fears when he took a meeker stance against not just Clinton but also Joe Biden. Hours earlier, he apologized to the former vice president after a surrogate accused Biden of having “a big corruption problem.”

The Biden walk-back and the subsequent Clinton sidestep, campaign veteran Matt Bennett suspects, was a strategic retreat. “Somebody probably got rattled inside the campaign with the Biden thing. I don’t think what he did with Clinton was all that remarkable; it would have been stupid to engage in a fight with her,” said the executive vice president of Third Way Strategies, a center-left think tank.

“He was already fighting with Warren and Biden,” continued Bennett. “I don’t think he could handle a third front in these wars.” The Biden apology must have come, in his estimation, because the Sanders camp likely “decided that strategically they were in a bad place and he had to clean it up.”

The cease fire was short-lived. With Sanders stuck in the Senate and Biden campaigning in Iowa, the former vice president released a video Tuesday night accusing the senator of “dishonest attacks” concerning Social Security. The Sanders campaign later released its own video while the senator was stuck on the Senate floor.

Impeachment has become a strategic challenge for Sanders and his colleagues still competing for the nomination. They are torn between fulfilling constitutional duty and pursuing presidential ambition as they leave the trail for jury duty. Competitors unburdened by impeachment obligations have clearly taken advantage.

According to the RealClearPolitics average, Biden leads in Iowa, where the first Democratic nominating caucus is just weeks away. Sanders, meanwhile, remains silent in the Senate and second in the race.