MILWAUKEE (Reuters) - Donald Trump's Republican Party convenes on Monday hoping to chart his return to the White House after he survived an assassination attempt that prompted him and President Joe Biden, his Democratic rival, to call for national unity and calm.

The former president will announce at the convention this week his choice for a running mate, having cited as frontrunners Ohio U.S. Senator J.D. Vance, Florida U.S. Senator Marco Rubio and North Dakota Governor Doug Burgum, all of whom will speak at the at the gathering.

Trump held individual meetings with each of the three men late last week in what was effectively one last job interview, according to two sources who requested anonymity to disclose private conversations.

While the event in Milwaukee, Wisconsin, will be a festive affair to formally choose the party's presidential nominee, it occurs at a tense moment in U.S. history on the road to the Nov. 5 election rematch between Biden, 81, and Trump, 78.

Will party leaders scheduled to speak over the next four days try to cool tempers among Republicans? Or will they use the occasion to accuse Democrats of demonizing Trump as a threat to democracy and making him a target for political violence?

"This is a chance to bring the whole country, even the whole world, together. The speech will be a lot different, a lot different than it would've been two days ago," Trump told the Washington Examiner.

Biden, too, in a televised address from the White House on Sunday, said: "There is no place in America for this kind of violence, for any violence ever. Period. No exceptions. We can't allow this violence to be normalized."

He said: "The political rhetoric in this country has gotten very heated. It's time to cool it down."

Trump and Biden are locked in a close election rematch, according to most opinion polls including by Reuters/Ipsos. The shooting on Saturday whipsawed discussion around the presidential campaign, which had been focused on whether Biden should drop out following a halting June 27 debate performance.

House Speaker Mike Johnson, the country's highest-ranking Republican, told NBC's "Today" show on Sunday that all Americans needed to tone down their rhetoric. He accused Biden's campaign of making hyperbolic attacks on Trump.

"Everyone needs to turn the rhetoric down," he said.

Biden condemned the assassination attempt. He ordered an investigation into Saturday's shooting at a rally in Butler, Pennsylvania in which Trump's right ear was grazed by a bullet, one supporter was killed and two others were wounded before Secret Service agents shot dead the 20-year-old suspected gunman whose motive has yet to be clarified.

The Biden campaign declined to comment on allegations from some Republicans that his comments helped created the conditions for the shooting.

Trump has frequently turned to violent rhetoric in his campaign speeches, using the word "bloodbath", labeling his perceived enemies as "vermin" and "fascists," and accusing Biden without evidence of a conspiracy to overthrow the United States by encouraging illegal immigration.

For Trump, the convention represents a test.

Having consolidated party control, Trump could seize on the prime time opportunity to deliver a unifying message or paint a dark portrait of a nation under siege by a corrupt leftist elite, as he has done at times on the trail.

"Trump's convention speech is going to be his introduction to the general public, to the people who aren't following politics closely. I think he will have even more eyeballs on him (because of the assassination attempt)," said Nachama Soloveichik, a Republican strategist who worked on Nikki Haley's unsuccessful 2024 presidential campaign.

"I would say the message should be one of de-escalation and also reminding people that America is better than that."

In an internal memo to campaign staff on Sunday, which was obtained by Reuters, co-campaign managers Chris LaCivita and Susie Wiles said the campaign would adopt additional security measures in the wake of the assassination attempt. They also called on staff to refrain from using "dangerous rhetoric."

"We condemn all forms of violence, and will not tolerate dangerous rhetoric on social media," they wrote.

VICE PRESIDENTIAL MYSTERY

As with previous conventions, a who's who of prominent Republicans, including media personalities and members of Congress, are slotted to speak.

They range from relative moderates to apologists for the Jan. 6, 2021, attack on the U.S. Capitol by Trump supporters and hard-right firebrands who have expressed support for conspiracy theories and are divisive even within the party.

The first three days of the event are organized around broad themes, with Monday focused on economic issues, Tuesday focused on public safety and Wednesday focused on national security.

Republicans are expected to portray America as more prosperous, less crime-ridden and less vulnerable to threats abroad during Trump's 2017-2021 term than it is under Biden, though the record is decidedly mixed and difficult to compare given that the coronavirus pandemic had an impact on both the Biden and Trump presidencies in different ways.

Milwaukee will play a key role in the Nov. 5 election given that it is the biggest city in Wisconsin, one of the most politically competitive states in the country.

By Sunday afternoon, security barricades around Fiserv Forum, the basketball arena where the convention's main activities will take place, had shut down much of the city's downtown. Thousands of armed law enforcement agents roamed streets that were otherwise largely empty as delegates streamed in from around the country.

Audrey Gibson-Cicchino, the RNC's liaison with the Secret Service, said security plans had not been changed for the convention, despite the assassination attempt on Trump.

"We are confident in the security plans for this event and we are ready to go," she told reporters on Sunday afternoon.

(Reporting by Gram Slattery and Tim Reid; Additional reporting by Nathan Layne; Editing by Ross Colvin and Howard Goller)

By Gram Slattery and Tim Reid