Trump is nearing a deadline to announce his running mate but appears in no rush as much of the attention is still centered on questions about Biden's ability to govern for another four-year term. Some Democrats have started calling for Biden to step down as their presumptive nominee following his dismal debate performance last month.

Both Biden, 81, and Trump, 78, are at least two decades older than most American presidents have been, according to the Pew Research Center, which said the median age for all U.S. presidents on their first inauguration is 55 years old. But that has not stopped Trump from arguing he is stronger than Biden, who repeatedly stumbled, paused and could not complete sentences at times during the June 27 debate. Trump was criticized by Democrats for making false statements during the debate about the Jan. 6, 2021, riot at the U.S. Capitol and suggesting immigrants entering the U.S. illegally were taking so-called "Black jobs" and "Hispanic jobs."

In an interview Monday with Fox News Channel's Sean Hannity, Trump said he thought Biden "might very well stay in" the race. "Nobody to wants to give that up that way," Trump added. "He is going to feel badly about himself for a long time. It's hard to give it up that way, the way where they're trying to force him out."

In the Miami suburb of Doral, Trump will underscore his strong support in a former battleground state that has now shifted toward the GOP. U.S. Sen. Marco Rubio, a Miami native and one of the contenders for the vice presidential post, will be attending the rally along with other Florida politicians.

Kevin Cabrera, a Miami-Dade County commissioner who was Florida state director for Trump's 2020 reelection campaign and is set to speak at the rally, said to expect an "overwhelming show of unity."

"The rally will display our unified front, showcasing a stark contrast to the Democrats, who are lost and fighting with each other over Biden's health and ability to continue," Cabrera said.

The presumptive GOP nominee will also touch on Biden's handling of immigration and the economy, highlighting the rise in home prices and goods. Trump will also talk about how Florida is affected by the increasing arrivals of immigrants as the final destination for many people illegally crossing the U.S.-Mexico border.

The leadership crisis among Democrats has perhaps given Trump a reason to wait for his VP announcement so as to not draw attention away from Biden's woes. Senior advisers and key allies say they still don't know whom Trump will choose as his running mate, and many believe the choice is still in flux.

Speaking on MSNBC Monday, Biden criticized Trump for not having held events since the debate and suggested he had been "riding around in his golf cart."