MILWAUKEE, Jul. 18 (Reuters) - 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 in Milwaukee, 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 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 party's 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 are part of a Democratic conspiracy, warned that Biden would usher in "World War Three" and described an "invasion" of migrants over the southern border.

As he has done throughout his political career, Trump argued that only he can save a dwindling nation from certain doom.
The speech capped a four-day event in which he was greeted with adulation by a party that now appears entirely in his thrall.

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

His entrance was befitting of a TV star or a pro wrestler - a screen lifted slowly to reveal Trump standing in front of massive lights arranged to spell out his last name before an image of the White House was projected behind him.

Trump's opponent in the Nov. 5 election, meanwhile, Democratic President Joe Biden, was "soul searching" about whether to drop out of the race entirely, 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.

Before Trump was due to take the stage for his keynote address, the convention paused to welcome his wife, Melania Trump, who has rarely been seen during the campaign. She entered the arena to classical music and waved to the crowd from a box next to Trump's vice presidential pick, Senator J.D. Vance.
Vance, at 39 half Trump's age, is widely seen as the ideological heir to Trump's Make American Great Movement.

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

Some of the eclectic group of speakers - including conservative commentator Tucker Carlson, who received a huge ovation, and Trump's son Eric - employed heated 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.

Opinion polls show four of the seven most competitive states looking increasingly out of reach for Biden. The Trump campaign, meanwhile, said it believes it is now competitive in Democratic-leaning states including Minnesota, New Hampshire, and Virginia.

Former President Barack Obama has told others that Biden, who was Obama's vice president, should rethink his candidacy, the Washington Post reported, citing anonymous sources.

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.