WASHINGTON — The most ardent supporters of Senator Bernie Sanders have long been outspoken about their anger toward Republicans — and in some cases toward Democrats. Their idol, the senator from Vermont, has called President Trump a “demagogue” and said recently that he was “perhaps the worst and most dangerous president in the history of our country.”

Now, in Mr. Sanders’s world, his fans have something concrete to grapple with: James T. Hodgkinson, a former volunteer for Mr. Sanders’s presidential campaign, is suspected of opening fire on Republican lawmakers practicing baseball in Alexandria, Va.

That shooting on Wednesday, which wounded four people, may prove to be an unexpected test for a movement born out of Mr. Sanders’s left-wing, populist politics and a moment for liberals to figure out how to balance anger at Mr. Trump with inciting violence.

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“Both sides need to look in the mirror,” said Nina Turner, a former Ohio state senator who campaigned for Mr. Sanders and is working on a new think tank started by the senator’s wife. “We have to decide what kind of language we are going to use in our political discourse.”

Mr. Sanders has advocated what he has called a peaceful political revolution. On Wednesday, he acknowledged that Mr. Hodgkinson, 66, of Belleville, Ill., had been a volunteer on his campaign and said he was praying for the recovery of Representative Steve Scalise, Republican of Louisiana, and the other victims.

“I am sickened by this despicable act,” Mr. Sanders said in a statement. “Let me be as clear as I can be. Violence of any kind is unacceptable in our society, and I condemn this action in the strongest possible terms. Real change can only come about through nonviolent action, and anything else runs against our most deeply held American values.”

His most prominent followers said that blaming all of Mr. Sanders’s supporters for the actions of one was akin to blaming all Muslims for the actions of the Islamic State.

“It doesn’t make sense to me, not with this shooting and not with blaming an entire Black Lives Matter movement when a random black man shoots a police officer,” said Shaun King, a columnist for The New York Daily News who campaigned for Mr. Sanders.

He added that violence would not help move liberal policies forward: “If 20 Republican congressmen were shot and killed, it would not improve the chances of us having a better health care system. It’s nonsensical.”

To be sure, supporters of Mr. Trump, as well as Mr. Trump himself, have assailed opponents and the news media.

But long before the shooting on Wednesday, some of Mr. Sanders’s supporters had earned a belligerent reputation for their criticism of Hillary Clinton, the Democratic Party and others who they believed disagreed with their ideas. Sanders fans, sometimes referred to derogatorily as “Bernie Bros” or “Bernie Bots,” at times harassed reporters covering Mr. Sanders and flooded social media with angry posts directed at the “corporate media,” a term often used by the senator.

The suspect in the shooting in Virginia put a new spotlight on the rage buried in some corners of the progressive left.

Mr. Hodgkinson filled his Facebook page with photographs of the senator and quotes from his speeches. Mr. Hodgkinson also wrote messages filled with expletives directed at the president, and a post in March said: “Trump is a traitor. Trump has destroyed our democracy. It’s time to destroy Trump & co.”

On Tuesday, Mr. Hodgkinson posted a cartoon on Facebook explaining “How does a bill work?” “That’s an easy one, Billy,” the cartoon reads. “Corporations write the bill and then bribe Congress until it becomes law.”

“That’s Exactly How It Works. ….” Mr. Hodgkinson wrote.

That is not far from Mr. Sanders’s own message. On Saturday, during a conference in Chicago filled with Sanders supporters, he thundered, “Today in the White House, we have perhaps the worst and most dangerous president in the history of our country,” to cheers from thousands. “And we also have, not to be forgotten, extreme right-wing leadership in the U.S. House and the U.S. Senate.”

Adam Lassila, 30, of Athens, Ga., who attended the conference, said Mr. Sanders’s criticism of Mr. Trump was justified and illustrated that the senator represented “the kind of politicians that we want in this society, those who describe things how they are actually happening and not speak around them in platitudes.”

For conservatives, Wednesday’s attack was a moment to say, “Enough.” In 2010, as the Tea Party movement rose, often with violent messages, Democratic lawmakers lamented the threats they faced. Republicans are feeling a similar lash as the left rises to confront a Republican president.

Harlan Hill, a political consultant based in New York who supports Mr. Trump, said people should not blame Mr. Sanders personally, but he said the senator’s description of the president as “dangerous” illustrated the “apocalyptic terms” and “melodrama” that have created a combustible political atmosphere.

“It is a passive justification for the kind of violence we saw,” Mr. Hill said. “If you don’t believe that, and you’re just casually using these words, then you should accept the consequence of those words because you are empowering the people that follow you to take whatever sort of action that they deem necessary to avert what is being described to them as a potential genocidal leader.”

While Mr. Trump was restrained in his remarks about the shooting, other figures on the political right let loose. Michael Savage, a radio host, wrote on Twitter, “I warned America the Dems constant drumbeat of hatred would lead to violence!” Bill Mitchell, a radio host who supports Mr. Trump, said on Twitter, “The Left in this country is ushering in a new #CultureOfViolence where violent hate is the new normal.”

RoseAnn DeMoro, the executive director of National Nurses United, a union that campaigned heavily for Mr. Sanders and continues to work with him, said some were hoping to discredit Mr. Sanders to slow down the continuing success of his brand of politics. She called it a “boldface lie” to connect the shooting to Mr. Sanders’s push for opposing Mr. Trump’s proposals.

“He’s the most popular politician in America,” Ms. DeMoro said of Mr. Sanders. “That doesn’t sit well with establishment Democrats or Republicans. They are trying to delegitimize and discredit anyone who is speaking out for a better society. That’s what’s happening.”