Donald Trump's running mate will have to correctly answer two key questions if they want to find their name on the ticket, his former national security advisor revealed. 

As speculation swirls around who the former president might select as his vice-president, John Bolton, who served under the ex-president between March 2018 and September 2019, revealed Trump's decision will hinge on just one decisive issue: the last election. 

'I'm afraid that the vice presidential interview questionnaire has only two questions on it,' Bolton told CNN's Kaitlan Collins, adding that Trump's 'highest priority is absolute personal loyalty to him.' 

He said the first question would be: 'Do you think the 2020 election was stolen?' 

Leading on from the first, he speculated that Trump would then ask: 'If I told you to do what I told Mike Pence to do on January 6, would you do it?'

Bolton, who became a frequent Trump critic after leaving his White House, said the candidates on Trump's VP shortlist would need to answer yes to both questions to 'make it into the finals.' 

'And if they're a no, you're out of it,' he added. 

Bolton felt that it would take a 'great loss of integrity' to fall in line behind Trump, and warned them that any early promises to be on the Republican ticket aren't to be trusted, because 'with Trump, it's never final until it's final.' 

It came as Trump appeared to tease at a rally in Miami on Tuesday night that he could pick Florida Senator Marco Rubio, who has seemingly found himself in the final shortlist. 

Trump repeatedly name-dropped Rubio during his rally, as he said there has been a 'lot of press' around the former presidential candidate's prospects. 

'They’ll probably be thinking that I’ll be announcing Rubio as my vice president,' Trump even admitted at one stage. 

He also prodded Rubio over his policy proposal to remove taxes from tips if he regains the White House, and told him that 'you may or may not be there to vote for it - but you'll be involved.' 

Trump's running mate roster is also believed to include Ohio Senator J.D. Vance and North Dakota Governor Doug Burgum, with outside names Vivek Ramaswamy and Byron Donalds also floated in recent months. 

In recent days, a DailyMail.com poll found that South Carolina Senator Tim Scott led the pack at 13 percent support, with Rubio in second at 12 percent tied with former Trump cabinet member Ben Carson.  

Trump has frequently said he will announce his running mate at the Republican National Convention in Milwaukee next week, however Bolton said he may break from tradition and hold off because of the negative press cycle surrounding President Biden. 

'Look, there's no news coming out of the Republican National Convention, other than the vice presidential nomination,' Bolton concluded. 

'Why waste it in a week when the Democrats may still be talking about whether Joe Biden's competent to be president?' 

Trump used the occasion to introduce his son Barron to his adoring crowd, receiving raucous applause as he announced, 'Welcome to the scene, Barron.' 

The former president joked that his son 'had such a nice, easy life - now it's a little bit changed,' and the 6-foot-9 teen was seen pumping his fist to the crowd in typical Trump fashion. 

'Where is Barron? Stand up. Look at him! You're pretty popular,' Trump said from the stage, where he was joined by a number of Republican figureheads including Florida Senator Rick Scott. 

Trump went on to issue several challenges to Biden, first saying he wants to debate the 81-year-old ahead of their next scheduled bout on September 10. 

He then challenged Biden to a golf match and staked $1 million on the game, while offering to give the president a 20-shot handicap after they sparred over their golf games at the debate. 

'I'm also officially challenging Crooked Joe to an 18-hole golf match right here. On Doral's Blue Monster considered one of the greatest tournament golf courses anywhere in the world,' Trump said. 'It will be among the most-watched sporting events in history.

'And if he wins I will give the charity of his choice - any charity that he wants - 10 million dollars,' the ex-president added. 'And I bet he doesn't take the offer.'

The Biden campaign quickly clapped back, calling Trump's rally 'deranged.'

'Joe Biden doesn't have time for Donald Trump's weird antics – he's busy leading America and defending the free world,' said campaign spokesperson James Singer.

Singer noted that Trump's rally consisted of the ex-president 'inviting fictional serial killers to dinner, teasing lil' Marco Rubio, praising Project 2025 architect Tom Homan, and challenging the President of the United States to golf.'

Analysts and pundits noted that Trump was unusually restrained following Biden's disastrous debate performance against him, which sparked furious speculation that Democrats could look to replace the 81-year-old before November's election. 

Biden's every move has come under scrutiny following the debate, and his speech to NATO leaders on Tuesday was his latest chance to dispel rumors he is too old for another four years in the White House. 

The octogenarian president narrowly avoided a near disastrous slip-up during his welcome speech, although he read a three-word instruction to himself as he visibly read from a teleprompter. 

As he awarded the Presidential Medal of Freedom to NATO Secretary-General Jens Stoltenberg, Biden was seemingly saved from utter embarrassment by the audience applause, as he declared: 'Ask the military aide.' 

Biden then quickly caught himself, while the crowd drowned up the flub with cheers.

'Military come forward,' he said. He proceeded to award the medal, hanging it around Stoltenberg's neck, without incident.

With a growing number of congressional Democrats calling for Biden to step aside, many pointed to Vice President Kamala Harris as his natural successor to take on Trump. 

With speculation falling on Harris' potential candidacy, several Democrats have been named as potential running mates if she had to step up to the top of the ticket. 

As the first black and Asian American female presidential nominee of a major party if Biden were to drop out, analysts believe she would need a running mate who looks like nearly all the former presidents to temper any shocks to identity politics. 

Among the names being floated are Governors Roy Cooper of North Carolina, Andy Beshear of Kentucky and Josh Shapiro of Pennsylvania, two people close to the Biden-Harris campaign told the New York Times.