NEWTON, Iowa — Sen. Bernie Sanders has begun framing his advanced age as an asset in the presidential race, an effort to counter concerns about his health with a pitch for voters to consider his decades of activism as they compare him with younger candidates.

On his first extended campaign swing since his Oct. 1 heart attack, the 78-year-old Vermont independent is being unusually candid about his age. At a town hall meeting Thursday, Sanders, unprompted, told voters, “I’ve been criticized for being old. I plead guilty. I am old. But there are advantages to being old.”

He elaborated at a news conference here Friday. “The ideas that I am fighting for now didn’t come to me yesterday,” he said in response to a reporter’s question. In case the point wasn’t clear, he added, “I’ve been on more picket lines, I expect, than all my opponents combined over the last 30 years.”

The impassioned comments, in an early nominating state that his advisers believe is crucial to his chances, represent a shift since his health scare. After taking two weeks away from the trail to recover, Sanders has resumed his busy schedule with a four-day swing through three states, concluding Sunday in Michigan.

While his remarks have often been in line with his earlier focus on such issues as income inequality and the need for universal health care, the greater attention to his age is a notable turn for a candidate who typically does not like to talk about himself and an attempt to create an implicit contrast with rivals who came to left-leaning ideas more recently.

“Having a long record gives people the understanding that these ideas that I am talking about — they are in my guts. They are in my heart,” he said Friday. “This is who I am as a human being, and it ain’t gonna change.”

Sanders’s aides played down the notion that his words amount to a concerted new strategy, saying they have personally heard him say similar things in the past. But publicly, the candidate is emphasizing his age in a new way, a message that appeared to play well with his crowds.

It is unclear whether Sanders will continue addressing his age so frankly. At the outset of his campaign, he spoke more frequently about his personal story on the advice of aides, but those lines soon disappeared from his speeches.

Sanders is now at third place in most polls, behind former vice president Joe Biden and Sen. Elizabeth Warren (D-Mass.). Biden, 76, and Warren, 70, have also faced questions about their age, but the subject is showing signs of becoming a larger concern for Sanders, especially since his heart attack.

Forty-three percent of Democrats in early battleground states said Sanders was too old to serve effectively as president, according to an October CBS News/YouGov poll, up from 37 percent in September. Twenty-eight percent said the same of Biden and just 4 percent of Warren.

Sanders is not the first presidential candidate forced to deflect questions about his age. In the 2008 campaign, Republican John McCain, then 71, would sometimes say, “I’m older than dirt and have more scars than Frankenstein, but I’ve learned a few things along the way.”

In 1984, GOP President Ronald Reagan, seeking re-election at 73, was asked about his age during a debate with Democrat Walter Mondale, 56. Reagan joked that “I am not going to exploit, for political purposes, my opponent’s youth and inexperience.”

Even before Sanders’s heart attack, a core part of his strategy was to emphasize that he is the candidate who could be most trusted to deliver a sweeping liberal agenda. He frequently points out, as he did Thursday in Marshalltown, Iowa, that he has been championing ideas such as single-payer health care long before they were in vogue in the Democratic Party.

Now Sanders is using the heightened focus on his age to underline that pitch.

“I do not go around this country disparaging other Democratic candidates,” Sanders said Thursday. But he added, “What distinguishes my candidacy from the others is I have been fighting for the working families of this country for many, many decades.”

During his current swing through Iowa, Sanders has also spoken directly, if briefly, about his heart attack. One man told the senator at Thursday’s town hall that he had suffered multiple heart attacks, adding that heart conditions can be overcome.

“I learned more about cardiology in the last couple weeks than I knew much about in my life,” Sanders responded. “It turns out about a million people per year have the procedure that you and I had.”

Still, Sanders has yet to provide details about how much damage his heart sustained. His campaign has vowed to release his health records before the end of the year.

Sanders’s allies are also hopeful that recent high-profile endorsements from a pair of young, liberal congresswomen will infuse his campaign with a more youthful image. Sanders plans to hold a rally with another potential endorser, Rep. Rashida Tlaib (D-Mich.), in Detroit on Sunday and a similar event with Rep. Ilhan Omar (D-Minn.) in Minneapolis early next month. Omar endorsed Sanders last week; Rep. Alexandria Ocasio-Cortez (D-N.Y.) was the other to do so.

Many of the voters showing up to support him appear to be accepting his new message. “Wisdom comes with age — you don’t start out that smart,” said Raymond Langloss, 57, who wore a “Bernie beats Trump” button to the Marshalltown town hall.

The bigger question for Sanders is whether he can win undecided voters such as Mary Stevens, 70, who said she is choosing among six Democratic candidates. “This is a very strenuous activity. He’s 78 years old,” said Stevens, who also attended the town hall. She added, “He took care of himself. He obviously is in good shape.”

Even before his heart attack, Sanders often answered questions about his age by saying it was only one of many factors voters should consider. He reprised that on Friday, saying there are many candidates who are young and vigorous but embrace bad policies.

“This is not a beauty contest,” Sanders said, adding jokingly, “which obviously I would win.”