Milwaukee, Wisconsin - Donald Trump predicted an "incredible victory" Thursday in accepting the Republican presidential nomination from a party euphoric over his escape from assassination and buoyed by the apparent implosion of Joe Biden's reelection campaign.

"We will have an incredible victory, and we will begin the four greatest years in the history of our country," Trump (78) said at the Republican National Convention in Milwaukee.

It was his first speech since a 20-year-old man shot at him, causing a wound to one ear and killing a bystander during a rally last weekend.

In a retelling of the shooting, where Trump said he had "God on my side," the ex-president asked for a moment of silence to honor the victim, firefighter Corey Comperatore. Before a hushed crowd, he kissed the slain firefighter's helmet on the stage.

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Trump took the stage to chants of "USA" from a crowd which has spent the week talking of him in near-divine terms.

Warm-up acts included shirt-ripping 1980s wrestling icon Hulk Hogan and conspiracy theorist and far-right media guru Tucker Carlson, who described Trump's survival as a historic moment.

After the assassination attempt, Trump became "leader of a nation," Carlson said.

But while the speech had been touted as the launch of a less abrasive, more unity-seeking Trump, he soon reverted to his familiar painting of America as an apocalyptic ruin that needs saving.

Promising to complete a wall on the US-Mexico border, he said an "invasion" of immigrants had brought "destruction" and "misery" to a "nation in decline."

He vowed to end Biden's massive spending on fighting climate change, calling it a "scam."

He again made his false claim that Democrats cheated in his defeat to Biden in the 2020 election. And, despite aides promising that Trump would not even say Biden's name in the speech, Trump did refer to his opponent and "the damage" he has done.

Despite a torrent of scandals, impeachment for his unprecedented attempt to overturn the 2020 election, and 34 felony convictions in May at a New York criminal trial, Trump is on the rise in polls ahead of November.

Now, with Republicans more in step behind him than ever, he is bullish about a shock return to power.

Attempting to flip the script on accusations that he intends to rule as an authoritarian leader, Trump insisted that he is "the one saving democracy" and referred to his criminal investigations as "witch hunts."

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"We must not criminalize dissent," he said.

Trump's love-fest in Milwaukee contrasted with the crisis engulfing Biden (81).

The Democratic president looked close late Thursday to being forced by his own party to withdraw and make way for Vice President Kamala Harris or another candidate, as fears spiral that his faltering physical health will lead to a loss in November.

Senior Trump advisor Jason Miller told AFP that "nothing fundamentally changes" for Trump if Biden drops out.

Trump's family was in attendance in Milwaukee, with son Eric rousing the crowd into a chant of "fight, fight, fight!"

Trump's wife Melania, who has been mostly absent throughout the campaign, arrived to applause but did not speak – a remarkable break with political convention at such events.

Supporters have been lining up all week to applaud the former president since the weekend attack by a gunman at a Pennsylvania rally.

Others addressing the convention included Trump's longtime friend Dana White, chief executive of the Ultimate Fighting Championship. Trump has attended multiple UFC bouts as he seeks to lock in younger male voters.

Striking a different tone, evangelist preacher Franklin Graham – whose father was spiritual adviser to multiple presidents – led a lengthy prayer for Trump.

With Biden still reeling from the aftermath of his disastrous debate performance against Trump last month, polls show a gap gradually opening in the long-close race.

The Republican campaign has even been talking up Trump's chances in Democratic strongholds like Minnesota and Virginia.

This week also saw Trump name right-wing Senator J.D. Vance of Ohio as his running mate.

The 39-year-old author of Hillbilly Elegy, a best-selling memoir about growing up poor in working-class America, is a former Trump critic who has become one of his staunchest backers.