MILWAUKEE/REHOBOTH BEACH, Delaware -- Donald Trump described on Thursday how he narrowly survived an attempt on his life, telling a rapt audience at the Republican National Convention in his first speech since the attack that he was only there "by the grace of Almighty God."

"I heard a loud whizzing sound and felt something hit me really, really hard on my right ear," he said during a 14-minute account, a thick bandage still covering his ear. "I said to myself, 'Wow, what was that? It can only be a bullet."

When he told the Milwaukee crowd that he was "not supposed to be here," the delegates chanted back, "Yes you are!" With photos of a bloodied Trump showing on screens behind him, Trump praised the Secret Service agents that rushed to his side and paid tribute to the volunteer firefighter who was killed, Corey Comperatore, kissing his fire helmet.

The former president struck an unusually conciliatory tone during the speech's opening moments, when he formally accepted the Republican presidential nomination.

"I am running to be president for all of America, not half of America, because there is no victory in winning for half of America," he said, in a marked shift in tenor for the typically bellicose former president.

But he swiftly pivoted to well-worn attacks on the Biden administration, which he said was "destroying" the country. He claimed without evidence that his criminal indictments were part of a Democratic conspiracy, predicted that Democratic President Joe Biden would usher in "World War Three" and described what he called an "invasion" of migrants over the southern border.

In the meandering remarks that followed - at 90-plus minutes the longest convention speech in history - Trump abandoned the message of unity he had promised to embrace in favor of his usual mixture of bombast and grievance, repeating his false claim that Democrats stole the 2020 election.

Trump asserted, as he has throughout his political career, that only he was capable of saving the country from certain doom.

"I could stop wars with a telephone call," he said.

The speech capped a four-day event during which he was greeted with adulation by a party now entirely in his thrall.

The convention's primetime program of speakers reflected the nominee's background as a reality television star: mixed martial arts executive Dana White, musician Kid Rock and pro wrestler Hulk Hogan, who fired up the crowd by tearing his top in half to reveal a sleeveless red Trump campaign shirt.

Trump's entrance was befitting of a pro wrestler - a screen lifted slowly to reveal him standing in front of massive lights arranged to spell out his last name, before a projected image of the White House appeared behind him.

Biden 'soul searching' about his campaign's future

Biden, his opponent in the Nov. 5 election, was meanwhile "soul searching" about whether to drop out of the race, one source said, after senior party figures, congressional allies and major donors warned him he could not win following a halting debate performance on June 27.

Biden, 81, was isolating at his Delaware home after contracting COVID-19. His doctor said he was experiencing mild symptoms.

Trump devoted much of his speech to attacking migrants, a theme that has always animated his presidential campaigns.

"They're coming from prisons, they're coming from jails, they're coming from mental institutions and insane asylums," he said, before citing by name several Americans who were murdered by suspects in the country illegally.

There is no evidence foreign governments are intentionally sending such people to the U.S. Academic studies show that immigrants do not commit crime at a higher rate than native-born Americans.

The speech broke Trump's own 2016 record for the longest delivered by a nominee, according to the American Presidency Project at the University of California in Santa Barbara. His 2020 convention address, delivered at the White House, was the third longest ever.

After Trump concluded, his family and that of his running mate, Senator J.D. Vance, walked onto the stage as balloons dropped from the ceiling. His wife Melania Trump, who is rarely seen on the campaign trail, joined him on Thursday for the first time this week.

Vance, at 39 half Trump's age, is widely seen as the ideological heir to Trump's Make America Great Movement.

"J.D., you're gonna be doing this for a long time," Trump said. "Enjoy the ride."

Trump tightens his grasp on the Party

Some of the eclectic group of speakers - including conservative commentator Tucker Carlson, who received a huge ovation, and Trump's son Eric - employed divisive language in denouncing the Biden administration.

The head pro at Trump's Florida golf club, John Nieporte, praised Trump's skills on the course and claimed the former president had won 21 club championships.

"Joe Biden? Zero," he said, evoking the surreal moment from the presidential debate when Trump and Biden argued over which of the two candidates had a better golf game.

With his grip on the Republican Party never tighter, Trump will be in a much stronger position than in his 2017-2021 term to follow through on his agenda if he wins the election.

Biden has faced increasing pressure from heavyweights in his party to cede his position at the top of the ticket. Former House of Representatives Speaker Nancy Pelosi is among those who have told him he cannot win in November, according to a White House source familiar with the matter.

After weeks of insisting that he will remain in the race, Biden is now taking calls to step aside seriously, and multiple Democratic officials think an exit is a matter of time, according to sources familiar with the matter.

Democratic leaders in the House and Senate - Hakeem Jeffries and Chuck Schumer - have told Biden directly that he will not only lose the White House but also endanger their effort to win back the House, according to reports in multiple news outlets.

Senator Jon Tester, who faces a challenging reelection battle in Montana this year, on Thursday became the 21st congressional Democrat and the second senator to publicly call on Biden to drop out.