Milwaukee, Wisconsin - Donald Trump received a hero's welcome Monday as he entered the Republican National Convention arena with a bandaged right ear in his first public appearance since being wounded in a weekend assassination attempt.

Hours after winning the formal nomination to be the Republican presidential candidate and announcing right-wing Ohio Senator J.D. Vance as his running mate, Trump marched into Milwaukee's Fiserv Forum flanked by aides and waved at supporters on the opening day of what is expected to be a triumphalist gathering.

Some 50,000 Republicans descended on the shores of Lake Michigan for the four-day convention, four months before election day.

Trump, who is due to give a formal acceptance speech on Thursday, took his seat to the sound of country singer Lee Greenwood's God Bless the USA without delivering any remarks, but appeared markedly moved by the rapt ovation he received from a packed venue.

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"It was absolutely amazing. I mean, just thinking what he's been through, and to come here today because he really cares," Illinois delegate Susan Sweeney told AFP on the convention floor.

It was the second huge moment of the day for the Republican crowd, which erupted into cheers earlier as Trump announced Vance as his vice presidential pick, rewarding a one-time harsh critic who has become one of his most uncompromising supporters.

Leading in multiple polls, Trump is exuding confidence.

At 81, Biden meanwhile is facing calls from his own side to quit the race over concerns around his age.

His faltering campaign released a statement saying the Trump-Vance agenda would "take away Americans' rights, hurt the middle class, and make life more expensive – all while benefiting the ultra-rich and greedy corporations."

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While Trump is increasingly confident of a shock return to the White House – despite being a convicted felon and facing multiple criminal trials, one of which was dismissed Monday – President Joe Biden is reeling from weak polls and Democratic concerns over his health.

The RNC takes place with the country reeling from a botched attempt by a gunman to kill Trump at a rally in Butler, Pennsylvania on Saturday.

The attack – which killed one bystander and left Trump with the bloodied ear that required the bandage – was expected to dominate proceedings.