Trump's VP announcement will come by next Monday: Adviser

Former President Donald Trump's long-awaited announcement on who his vice presidential pick will be could likely happen this week, senior adviser Jason Miller said on Monday.

"By this time next Monday, we will know who President Trump has selected as his running mate for the 2024 election," Miller said during a Monday appearance on Fox & Friends.

"It could happen any time this week. Could happen literally right up until the first day of the convention," he added, referencing the Republican National Convention, which kicks off next Monday.

He then waded into speculation that the Democratic ticket of President Joe Biden and Vice President Kamala Harris wouldn't be the ultimate Democratic ticket for November following calls for Biden to withdraw from the top of the ticket following the president's debate performance. In an exclusive interview with ABC News' George Stephanopoulos, Biden brushed off the poor performance as a "bad episode."

Though Miller wouldn't delve into specifics about Trump's list of potential vice presidential picks, he did contend that the former president has discussed potential running mates other than Sens. Marco Rubio and J.D. Vance and North Dakota Gov. Doug Burgum.

While campaigning in Philadelphia last month ahead of his debate with Biden, Trump claimed "in [his] mind" he had decided who his running mate would be.

Trump has long said he planned to make his announcement either at or right before next week's RNC in Milwaukee.

"Right around the convention, maybe a little before," he said while campaigning late last month.

The campaign has already begun solidifying preparations for Trump's running mate. A plane for the future Republican vice presidential nominee is already parked in an airport hanger, sources told ABC News; Trump's pick is already scheduled to be at a fundraiser next week in Milwaukee during the RNC, according to an invitation confirmed by ABC News.

However, campaign officials still maintain they don't know who Trump's final selection will be, and some of the people reported to be on his shortlist also claim not to have much information.

Vance said on NBC's "Meet the Press" on Sunday that he hasn't received a call from Trump asking to be his running mate. He said he is focusing on campaigning for Trump at the moment.

"I have not gotten the call, Kristen, and I'll certainly -- you know, maybe not the first person that I let know if that happened, but we'll let the media know if I ever get that call," Vance said. "But most importantly, Kristen, we're just trying to work to elect Donald Trump."

Rubio also said he has "heard nothing" about joining Trump's ticket.

"I heard nothing. I know nothing; you probably know more than I do about it. Donald Trump has a decision to make. He'll make it when he needs to make it. He'll make a good decision," said Rubio during an appearance on CNN's "State of the Union" on Sunday.

Trump and his campaign have seemingly enjoyed playing the waiting game on this announcement, offering them an opportunity to garner swirling media attention as well as a host of enthusiastic surrogates trying to break through to the No. 2 spot.

As time dwindles down for Trump's choice to eventually be made public, he and his campaign say they'll have to be ready to go.

"Whoever he does pick needs to be able to step in and do the job on Day 1. Each of the different prospects has their own strengths, and I think really can help chart the nation forward," said Miller on Fox Monday.