A Fired-Up Obama’s 2020 Job: Guarding Biden and Needling Trump

In those conversations, Mr. Obama outlined the role of “happy warrior,” of attacking Mr. Trump directly in a way he had never done before, but with the lacerating humor he employed during his two campaigns for president.

Some of his slaps are spontaneous, but many have been carefully workshopped — including the “Beijing Barry” line, which was delivered the day before the final presidential debate and was deployed to defuse Mr. Trump’s attacks on business deals in China pursued by Mr. Biden’s son Hunter, aides said.

Mr. Obama’s bellicose approach had another benefit that was not immediately evident until he began working on his remarks this month, according to Democratic aides.

The former president believed that taking on the classic bodyguard role embraced by Mike Pence and previous Democratic vice-presidential candidates would enable Mr. Biden’s running mate, Senator Kamala Harris, to avoid having to make those attacks herself and remain largely above the fray.

Yet for all of his continued popularity with Democratic voters, Mr. Obama is not on the ticket in 2020 — and his frenetic late campaigning on behalf of Mrs. Clinton did not prove decisive four years ago.

And his presence, especially in a complex state like Florida, is not universally positive.

”Obama’s Cuba policies were deeply unpopular with many voters in Southern Florida, and for all of his post-presidency popularity, he also carries some real liabilities,” said Alex Conant, a veteran political consultant who worked for Senator Marco Rubio, a Cuban-American Republican who opposed Mr. Obama’s attempt to normalize relations with the government in Havana.

“Obama’s always been skillful at driving a message and twisting a knife,” Mr. Conant added. “But his political capital wasn’t transferable when he was president, and it’s unclear if it is now.”