INDEPENDENCE, Iowa — Hundreds flocked to the sidewalks to watch this year's Fourth of July parade in Independence, Iowa, and catch a glimpse of several 2020 Democratic candidates.

But not all of the attendees were offering encouraging words.

As current primary front-runner Joe Biden jogged down the town's 2nd Street, he was met with cheers from supporters, as well as mockery from some critics.

"Where's your walker?" one spectator yelled, as others around him jeered "Trump, Trump" when Biden passed by.



Biden ran back and forth between parade goers to shake as many hands as possible. You could hear some “Trump” chants when his supporters were chanting Biden’s name pic.twitter.com/mF6trbtIGs — Marianna Sotomayor (@MariannaNBCNews) July 4, 2019

Another approached Biden, 76, during the parade and exclaimed "Sleepy Joe!" President Trump's derisive moniker, before the former vice president asked him to join him in a jog. The man declined.

Both former Texas Rep. Beto O'Rourke, 46, and New York City Mayor Bill de Blasio, 58, were also in attendance during the day's festivities. Neither of them, however, tried looking as fit and spry as Biden, who trotted for several blocks during the parade.

Biden's spirited effort to appear energized and lively left many of his decades-younger staffers stained with sweat and out of breath.

The question of whether Biden is physically up for the job as president has plagued his campaign since he announced in April.

A Reuters poll released Monday found that Americans care more about a president's age than his sexual orientation, with 48% of adults saying they were "much" or "somewhat" less likely to support a candidate if the individual was older than 70. Bernie Sanders is 77 and the next-youngest candidate behind Biden is Elizabeth Warren, who became a septuagenarian last month.

Biden's appearance in Independence marks only his third trip to Iowa during his third White House run. He dropped out after securing 0.9% of the vote in the 2008 Iowa caucuses and withdrew from the 1988 race in September 1987 following a plagiarism scandal.