Mr. Sanders on Tuesday night visited an outdoor memorial in Las Vegas that’s dedicated to victims of the city’s 2017 mass shooting. He also hosted a grass-roots fund-raiser at the Shiraz restaurant.
The restaurant’s owner, Raja Majid, said in a phone interview that Mr. Sanders spoke to a crowd of about 250 people. As he began taking questions from the audience, he asked a staff member, Ari Rabin-Havt, a deputy campaign manager, for a chair, an unusual request from a candidate who typically stands or paces onstage. “Ari, can you do me a favor?’’ Mr. Sanders said, according to a video posted on Periscope. “Where’s Ari? Get me a chair up here for a moment. I’m going to sit down here. It’s been a long day here.”
It is unclear whether Mr. Sanders will be able to participate in the next debate, scheduled for Oct. 15 in Columbus, Ohio.
Mr. Sanders’s allies quickly downplayed his procedure. RoseAnn DeMoro, a former leader of a nurse’s union and longtime Sanders surrogate, said “there are numerous presidents who have had heart problems and heart problems far worse” than what Mr. Sanders underwent Wednesday, adding that a stent “can improve one’s health.”
But many Democratic voters have long expressed discomfort with nominating a candidate in their 70s, and Mr. Sanders’s heart difficulties will likely refocus attention on age as a factor in a race where the three leading candidates are in their 70s. A Pew survey in May indicated that only 3 percent of Democratic voters believed the best age range for a president to be in was in their 70s. Forty-seven percent of those surveyed said they preferred a president in their 50s. One of Mr. Sanders’s chief rivals, Joseph R. Biden Jr., who is 76, has drawn attention to his age because of his sometimes rambling discourses and uneven answers at debates.
Mr. Sanders, who lost to Hillary Clinton in the 2016 Democratic primary, has been among the leaders in the Democratic primary since he entered the race in February. He was running second to Mr. Biden in most early polls but has fallen into third in recent weeks — behind Mr. Biden and Senator Elizabeth Warren — in several polls of early nominating states.
The Sanders campaign had planned to go on air with his first television ads of the campaign this week in Iowa, announcing a two-week $1.3 million buy on Tuesday. An ad tracking service, Medium Buying, said on Wednesday that Mr. Sanders began postponing those ads. The reason for the cancellation was not immediately known. Even as late as Tuesday night, Faiz Shakir, Mr. Sanders’s campaign manager, was talking excitedly about the ad buy on a call with supporters.