BURLINGTON, Vt. — Senator Bernie Sanders, in a striking concession for a leading presidential candidate, said on Tuesday that he planned to slow down his pace on the campaign trail after suffering a heart attack a week ago, and acknowledged that voters would likely consider his health when deciding whether to support him.
“I think we’re going to change the nature of the campaign a bit,” Mr. Sanders told reporters after a visit with a local cardiologist. “Make sure that I have the strength to do what I have to do.”
Mr. Sanders’s remarks stood in sharp contrast with comments in recent days from his campaign advisers, who have insisted that the Vermont senator was neither changing course nor easing his trademark intensity as a result of the heart attack.
Given Mr. Sanders’s influential role in the Democratic race, not only as a top candidate but also as a driving force in policy debates, his decision to pull back campaigning injects new uncertainty into the contest — both for the future of Mr. Sanders’s candidacy and the possible ramifications for other contenders.
In recent weeks, the race has become more of a two-person contest between Senator Elizabeth Warren, a fellow liberal who shares many of the same goals as Mr. Sanders, and former Vice President Joseph R. Biden Jr., whose policy positions are generally more moderate. Ms. Warren has risen steadily in many polls while both Mr. Biden and Mr. Sanders have lost some ground, particularly in surveys of Iowa voters, who will hold the first nominating contest in February.
Pollsters said on Tuesday that it was too soon to determine or measure the impact of Mr. Sanders’s health issues on voter preferences in the race, but they noted that his admission about his health would create a new challenge for Mr. Sanders, who, at 78, would be the oldest president ever elected by far.
“This will just raise the issue of his age, which to me has always been the Achilles’ heel of the Sanders campaign,” said Andrew Smith, director of the University of New Hampshire Survey Center, which polls public opinion in the key primary state. “When Sanders ran for president in 2016, he was the not-Hillary Clinton candidate and no one paid attention to how old he is. Now, there will be a lot of attention to how old he is, and how old Joe Biden is.”
Mr. Biden is 76, while Ms. Warren is 70. President Trump is 73.
Speaking to reporters outside his home in Burlington Tuesday, Mr. Sanders gave no indication that he was planning to drop out of the race and said he would continue to campaign actively. Indeed, Mr. Sanders remains formidable: He reported a third-quarter fund-raising total of $25.3 million, the largest in the Democratic field, and he has helped steer many in the party to embrace ideas like “Medicare for all” and tuition-free public colleges.
Mr. Sanders has been campaigning almost nonstop when not carrying out his Senate duties in Washington, D.C., a pace that he pointedly noted on Tuesday.
“We were doing, you know, in some cases five or six meetings a day, three or four rallies and town meetings and meeting with groups of people,” Mr. Sanders said. “I don’t think I’m going to do that.”
“I think we’re going to change the nature of the campaign a bit,” he added. “Make sure that I have the strength to do what I have to do.”
Asked to clarify what he meant when he said the campaign would change, he replied: “Probably not doing four rallies a day.”
Standing next to his wife, Jane, Mr. Sanders also acknowledged that his heart attack could be a factor for voters considering whether to support him.
“Everything that happens every day weighs on how people feel about you,” he said. “And my own view is that — and I think it’s the voters’ view — you look at the totality of who a candidate is. You look at what that candidate stands for, the integrity of that candidate, the history of that candidate.”
It has been a difficult week for the Sanders family: In addition to Mr. Sanders’s heart attack, his daughter-in-law Rainè Riggs died at age 46, shortly after she was diagnosed with neuroendocrine cancer, according to a death notice. Ms. Riggs was the wife of Levi Sanders, Mr. Sanders’s son.
Mr. Sanders’s campaign aides were heartened that the first polls since his hospitalization did not show a significant drop in his support. But the candidate and his wife have not been revealing much to the public, or even some of his own staff, about when he would get back to the campaign trail and how aggressive he would be once he does return.
It is now almost certain that he will have a far more difficult path to the nomination. Democrats are overwhelmingly focused on finding a candidate they believe can defeat Mr. Trump, having made clear in surveys that ousting a president they loathe is their top priority. Now, in addition to questions about whether he is too far to the left to win over general election voters, Mr. Sanders will have to face doubts about his physical capabilities.
Further, unlike in 2016, progressive voters have an alternative to Mr. Sanders in this race. While some of his bedrock supporters will not abandon him, other left-wing voters will gladly cast a vote for Ms. Warren. That was not the case when Mr. Sanders faced Mrs. Clinton in the last primary.
Mr. Sanders returned to Burlington over the weekend, after spending three days in a hospital in Las Vegas. His campaign said he felt chest pains during an event last Tuesday, and he was taken to the hospital, where two stents were inserted into an artery.
Since then, his campaign has insisted that Mr. Sanders does not intend to drop out of the race. During a telephone call with staff members on Monday, Mr. Sanders said he felt “more strongly about the need for a political revolution today than I did when I began this campaign.”
Jane Sanders, who remains one of Mr. Sanders’s closest advisers, said that idea was “something that the entire campaign, and especially me, have been saying for months — not for his health but for the ability to keep up that kind of a pace for everybody else, too.”
Campaign officials also downplayed Mr. Sanders’s remarks.
“As Bernie said, we are going to have an active campaign,” Faiz Shakir, Mr. Sanders’s campaign manager, said in a statement on Tuesday evening. “Instead of a breakneck series of events that lap the field, we are going to keep a marathoner’s pace that still manages to outrun everyone else.”
Another adviser, who spoke on the condition of anonymity to discuss a sensitive topic, said Mr. Sanders had been thinking about changing the pace of his campaign schedule for some time, and aides discussed this with him when he was in the hospital.
Known for keeping a grueling schedule on the campaign trail, Mr. Sanders, who finished second to Mrs. Clinton in the 2016 primary, will often crisscross a state with multiple stops for big rallies and smaller town hall-style events and gatherings.
There is no recent precedent for a candidate to suffer such a serious health setback in the midst of a campaign, at least not since President Dwight D. Eisenhower suffered a heart attack in the fall of 1955, a year before his re-election. Mrs. Clinton stayed off the campaign trail for three days in the fall of 2016 after she felt dizzy at a 9/11 commemoration but was only diagnosed with pneumonia.
In 1999, former Senator Bill Bradley was briefly sidelined as he sought the Democratic nomination because he had an irregular heartbeat. Mr. Bradley, a former professional basketball player who was only 56 at the time, returned to the campaign trail but was dogged by questions about his health and was beaten decisively by Al Gore.
Sydney Ember is a political reporter based in New York. She was previously a business reporter covering print and digital media. @melbournecoal
Jonathan Martin is a national political correspondent. He has reported on a range of topics, including the 2016 presidential election and several state and congressional races, while also writing for Sports, Food and the Book Review. He is also a CNN political analyst. @jmartnyt