Vivek Ramaswamy, speaking with reporters after his speech at the Heritage Policy Fest, joined Trump in stressing unity after the shooting at the former president's Pennsylvania rally.

ABC News asked Ramaswamy for his response to Republicans like J.D. Vance going after Democrats and President Joe Biden in the wake of the attempted assassination attempt.

"Look, I think that there is a lot of understandable anger. I was ... my first reaction was anger," Ramaswamy said. "And the reason my first reaction was anger was that the only thing more tragic than what happened on Saturday is that if we're being really honest with ourselves, all of us, it wasn't totally a shock, actually. And that, that is maddening. And that ... makes me angry as a citizen of the United States of America. But the question is, how do we channel that anger?"

Ramaswamy said Republicans have a "second chance that Lincoln didn't have: to unite a country that this time didn't have to fight a civil war, but avoids one."

"If that bullet hit Donald Trump, we'd be in a very different place now," he said. "And the fact that we've been given that chance, I think it's our responsibility to step up and seize it not by compromising on our principles, but by actually reviving the principles that unite all of us. And by seeing the enemy as the ideology that we're up against, rather than our fellow neighbors as our enemy combatants, and that's what I call on not only the Republican Party but every American to do in the wake of what happened on Saturday."

-ABC News' Alexandra Hutzler

As part of a plan that predates the assassination attempt on former President Donald Trump, roughly 1,700 National Guardsmen and several active-duty troops will assist other agencies with security at the Republican National Convention, according to Deputy Pentagon press secretary Sabrina Singh.

"In regards to the Republican National Convention, approximately 1,700 National Guard and a small number of active-duty personnel will be providing support to civil authorities from July 13 through 19. These personnel are supporting the FBI, U.S. Secret Service and Milwaukee Metro Police Department for 24/7 operations," Singh said.

Singh emphasized that this support was pre-planned, and not related to the shooting at Trump's rally over the weekend, nor was the force augmented as a result.

-Matt Seyler

Former President Donald Trump told Fox News' Bret Baier on Monday morning that he will announce his pick for vice president on Monday.

The decision will come after months of speculation about who his running mate will be.

There will be a roll call vote on the presidential ticket, which includes the vice president, on Monday at the RNC.

The attempted assassination of former President Donald Trump has thoroughly altered the stakes and tone of the Republican National Convention in Milwaukee, which kicks off Monday, just two days after a shooter opened fire at the former president's Pennsylvania rally on Saturday, grazing Trump's ear and leading to a spectator's death.

Trump arrived in Milwaukee Sunday afternoon, ahead of the RNC's start on Monday.

In a social media post Sunday, Trump indicated that he was going to delay his trip, but decided he wouldn't allow a "shooter" to change his scheduled plans to head to the RNC.

U.S. Secret Service and other officials said Sunday there are no plans to expand the security perimeter and that there are no known threats. Ahead of the shooting at his rally, the GOP convention was gearing up to be an extravagant event centered around symbolic, Trump-era Republican ideas and party unity, sealed on Thursday with the third nomination of the former president.

-ABC's Brittany Shepherd, Kelsey Walsh and Isabella Murray