News that Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) had been hospitalized so that two stents could be inserted to prevent an arterial blockage has Democrats fretting once again about the age of their leading contenders for the White House.

Sanders, 78, was in “good spirits” after the procedure, according to his campaign. Later on Wednesday, he turned his operation into an opportunity to tout “Medicare for All,” tweeting that he was feeling fine and was fortunate to have “great doctors and nurses helping me to recover.

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“None of us know when a medical emergency might affect us,” he said. “And no one should fear going bankrupt if it occurs. Medicare for All!” Sanders wrote.

Polls show Sanders is one of the top three candidates running for the Democratic presidential nomination, and all three are in their 70s.

Former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, 76, has repeatedly heard questions about his age amid verbal flubs and statements, such as a comment about listening to records during one of the Democratic debates, that underscore how he is of an older generation.

As questions came up about his age and stamina, some allies suggested to the campaign that Biden pace himself.

Sanders and Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.), 70, have heard fewer questions about their age, and Sanders supporters have pointed to their candidate's vigorous schedule and said he had no signs of slowing down. “He walks faster than I walk,” one Sanders ally told The Hill.

But questions for Sanders are likely to step up after Wednesday.

“You can be a young 78 but you’re still 78,” one longtime Democratic strategist wondered. “I think the Bernie news is proof of that.

“They’re all old,” the strategist continued. “Is this really the best we could do?”

Democrats will face off against a 73-year-old in President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE, who has also at times faced questions about his age.

Trump has also signaled his willingness to make age an issue in the campaign. He frequently goes after Biden and has argued the former vice president has lost a step.

Some Democrats have argued the party would be better off with a younger nominee.

“The best way for the Democratic Party to realize its growth potential is younger leadership,” said Democratic strategist Brad Bannon said. “It is limiting that the party’s most visible leaders, Sanders, Biden, Warren and [House Speaker Nancy] Pelosi are all in their seventies.

“Youth must be served and the party should be grooming a new generation of leadership,” he added.

Democrats remember how Republicans used health issues against 2016 presidential nominee Hillary Clinton Hillary Diane Rodham ClintonBloomberg rolls out M ad buy to boost Biden in Florida Hillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close Trump pledges to make Juneteenth a federal holiday, designate KKK a terrorist group in pitch to Black voters MORE.

“I have in mind all the questions about HRC's age, which were raised by many before Trump was her opponent,” one Democratic strategist said, referring to Clinton. “Trump then raised it often which many quickly dismissed because it was him.”

Clinton was seen collapsing while suffering from pneumonia after attending a 9/11 memorial in the final weeks of the campaign in 2016. Video of Clinton played on loop on the cable networks as Clinton aides scrambled to do damage control.

“That changed the conversation perhaps more than that incident should have,” the source said.

Julian Zelizer, a professor of history and public affairs at Princeton University, said the Sanders news will have an impact on the race.

“I think it hurts all the older candidates, but especially Biden since this keeps coming up,” Zelizer said. “It raises the questions and concerns of age and will go well beyond Sanders.

Zelizer said age has been an issue in past presidential cycles including in 1984 when Democratic presidential nominee Walter Mondale tried to use it against President Ronald Reagan. Mondale’s effort failed miserably when Reagan made a joke about not using Mondale’s inexperience against him in one of the most memorable moments from a presidential debate in U.S. history.

Democratic strategist Eddie Vale said he’s “not concerned at all” about the age discussion that has been interwoven in the primary discussion.

“Trump is basically the same age and spends all day eating cheeseburgers and has to even ride a golf cart onto the greens instead of walking,” Vale said.

“The best way that candidates can handle it — both in the primary and the general — is by showing that the age number itself is meaningless because what they DO is what matters,” Vale said.

Sanders has kept a rigorous campaign schedule. He was scheduled to make seven campaign stops in California on Thursday and Friday alone.

“Our field of candidates is criss-crossing the country doing a million events, parades, debates, interviews etc, while Trump, like he did during the last campaign, likes to do one big rally in the afternoon or evening so he can fly home to eat another cheeseburger in bed,” Vale said.

Sanders campaign officials did say the senator — who has won over millennial voters to his campaigns —would be taking a break from the campaign trail to recover from the heart procedure.

Sanders was expected to be in the hospital for one or two days, allies said.

“Sen. Sanders is conversing and in good spirits,” Jeff Weaver, a senior adviser to Sanders said in a statement on Wednesday. “We are canceling his events and appearances until further notice and we will continue to provide appropriate updates.”