U.S. President Joe Biden must drop his re-election bid or Donald Trump is sure to return to the White House, former Italian prime minister Matteo Renzi said on Wednesday.

Renzi, 49, led a centre-left government from 2014-2016 and was close to the administration led by former President Barack Obama, in which Biden was vice president. He was offered a lavish state dinner at the White House in 2016.

"Biden will go down in history as a U.S. president who did many things that had a great impact," Renzi told Reuters. "At the same time, if he does not quit he will give Trump the greatest gift he could ever receive."

With Biden as an opponent, Trump had an "open goal" for the presidency, Renzi said, using a soccer analogy. He said the Democrats still had time to build a credible campaign with another candidate.
"If they go with Joe, I fear it will be a lost battle," he said.

Renzi said a Trump presidency would have "unpredictable" consequences.

"Democrats must now do everything not to lose this battle. And the only way is to change horses," he said.

Romano Prodi, another centre-left former Italian premier and ex-president of the European Commission, was less blunt but similarly worried. Prodi, at 84, three years older than Biden, has long been retired from active politics.

"The only person who can decide whether Biden should stand down is Biden, but I saw the debate and I am very, very worried. I can see there is a growing concern about the situation among Americans, and I share that concern," he told Reuters.

Enrico Letta, a third former centre-left Italian prime minister, echoed those sentiments, telling Reuters he thought Biden should "pass the baton to someone younger", capable of countering the "deathly danger" of another Trump presidency.