ELKADER, Iowa (Reuters) - Former Vice President Joe Biden campaigned in Iowa on Friday with John Kerry, the former U.S. secretary of state and presidential nominee, seeking to bolster his case that he can set right a world turned topsy-turvy by President Donald Trump.

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Kerry, the Democratic presidential nominee in 2004, is the most significant endorsement for Biden so far in his quest for the party’s nomination to challenge Trump in the 2020 election. The two share a deep experience in global affairs, something Biden hopes will be an advantage against his Democratic rivals.

“The world is wondering what happened to America,” Kerry told a crowd in Elkader, Iowa.

Earlier, in Cedar Rapids, he warned “our whole world is at risk.”

Biden, who served as Barack Obama’s vice president, has argued that he is best positioned to repair traditional U.S. alliances that Trump has frayed.

Kerry served as the nation’s top diplomat during Obama’s second term. Biden and Kerry also served together for 24 years in the U.S. Senate, where both chaired the Senate Foreign Relations Committee.

Of their working relationship, Kerry joked, “The only team that has worked more closely than the two of us is Donald Trump and (Russian President) Vladimir Putin.”

Biden, he said, knows the “difference between our adversaries and our allies.”

Kerry’s endorsement, Biden said, “literally means the world to me.” He praised Kerry for his role in negotiating the Paris climate accord and the nuclear deal with Iran, pacts that Trump has abandoned.

Foreign policy has been central to Biden’s week as he has toured by bus though the early voting state of Iowa. His campaign cut a well-received Twitter video playing off Trump’s time at the NATO meeting in Britain, suggesting the president is a laughingstock to the rest of the world.

Also on Friday, a Super PAC supporting Biden, Unite the Country, said it would begin airing a pro-Biden ad in Iowa next week. The first Democratic nominating contest will be in Iowa on Feb. 3.

Biden, 77, has been trailing in opinion polls in Iowa behind Pete Buttigieg, the mayor of South Bend, Indiana, and U.S. Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont. The bus tour has marked his most intensive campaign effort yet in the state.

Kerry’s come-from-behind win in Iowa helped propel him to the 2004 Democratic presidential nomination. He lost the general election to President George W. Bush – the last time a Republican president was elected to a second term.

In Elkader, Biden noted that the caucuses were now fast approaching.

“Folks, it’s getting cuttin’ time here,” he said.