DES MOINES, Iowa — When Joe Biden was last in Iowa, his presidential campaign was on the verge of collapse and he was soundly trounced in the caucuses by a former Indiana mayor nearly 40 years his junior. He returns Friday as the Democratic nominee, believing he’s just days away from becoming president-elect.

Biden’s trip reflects the remarkable arc of his third presidential campaign. He entered the race as the most experienced candidate in a crowded primary, but was overshadowed by fresh faces who dazzled Democratic voters and nearly ran out of money.

But Democrats have rallied behind Biden as their best candidate to defeat President Donald Trump and unify a country facing health, economic and social crises. And the money woes that plagued Biden during the primary have vanished as he’s built a nearly two-to-one cash advantage over Trump that’s allowed him to flood the airwaves and make ambitious plays for states like Iowa, which flipped to Republican in 2016.

The dramatic nature of Biden’s rise is eclipsed only by the challenges faced by Trump — whose confidence in his reelection was dealt a devastating blow by the coronavirus pandemic this spring, with the public health and economic crises still rearing their heads in the days leading up to the close of polling.

“I don’t take anything for granted,” Biden told reporters Friday. “We’re gonna work for every single vote up ’til the last minute.”

With four days until the election and more than 80 million votes already cast, time is running out for Trump and Biden to change the shape of the race. Biden is leading most national polls and has a narrow advantage in many of the critical battlegrounds that could decide the race.

Friday marks the beginning of the critical final stretch before the election. Trump’s closing sprint to Election Day also includes four stops in Pennsylvania on Saturday and nearly a dozen events in the final 48 hours across states he carried in 2016.

After Iowa, Wisconsin and Minnesota on Friday, Biden will hit Michigan on Saturday, where he’ll hold a joint rally with former President Barack Obama.