It's a little over a month until the GOP has its convention and formally nominates Donald Trump for a third run at the White House, and while the contest for the top job just gets more interesting by the day, there is increasing speculation as to who Trump's understudy might be. While the former president seems pretty robust, his age would make picking a younger person for the VP slot a prudent choice. 

As of this week, there are a few more names on the list of possibilities. The Trump campaign has reached out to three more possibles, requesting vetting materials: Those three are Senator Marco Rubio (R-FL), North Dakota Governor Doug Burgum, and Senator J.D. Vance (R-OH). It's unclear precisely what information was requested.

Former President Donald Trump's campaign has begun the process of formally requesting information from a small handful of potential running mates, ABC News has learned, marking a significant escalation in the process that will result in Trump choosing a candidate for vice president.

Among those who have been asked by the campaign for vetting paperwork include North Dakota Gov. Doug Burgum and Sens. Marco Rubio and J.D. Vance, sources tell ABC News. The quiet outreach by campaign officials intensified last month, while Trump was consumed with his criminal hush-money trial, the sources said.

Others are likely to be considered for the No. 2 job, but the initial asks reflect who tops Trump's list at this point. Campaign officials say the final decision will be Trump's.

That last sentence is, perhaps, belaboring the obvious. 

Before this latest doc request, several other candidates were also asked to submit vetting documents.

Trump campaign officials have also requested information from Sen. Tim Scott, Reps. Byron Donalds and Elise Stefanik and Ben Carson, sources said. But it's unclear how extensive the requests were.

Representatives for Burgum and Vance did not respond to ABC's request for comment. Rubio denied that he had received any reach out from Trump campaign officials.

"I haven't talked to them about vice president," Rubio told ABC's Rachel Scott on Wednesday.

So, what conclusions can we draw from this? Probably none.

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There are a few things we can speculate on, though. While Trump isn't exactly soliciting input, there are a few qualities he ought to (and likely will) consider with this upcoming choice.

First, age. Ideally, the pick will be young, dynamic, and have plenty of energy. Donald Trump, while he appears to be in fine fettle for a man his age, is still, well, a man his age. Having a young VP who the nation can see as ready to step in should anything happen to POTUS is a plus.

Second, electability. Whoever Trump picks will be front-loaded, as it were, to run for POTUS in 2028. Whoever this person is, assuming that Team Trump wins in November (which is looking pretty likely), should walk into the veep's office on day one with that in mind; that is, unless Trump makes a Cheney-like choice of someone who has no intention of seeking that job.

Third, fortitude. A second Trump term will have to be able to absorb everything the Democrats and the legacy media throw at it, and it's going to be a s**tshow of Brobdignagian proportions. The VP will be subject to every attack, professional and personal, that anyone can dream up, and they better have the durability to weather that and still look confident going into 2028.

With all that said, there's a name on this list that is somewhat conspicuous by its absence: Florida Governor Ron DeSantis. In many ways, the Florida governor seems an obvious choice: one of, if not the most successful Republican governor in the country; he's tough, he's confident, he's capable, and he's one of the top contenders that comes to mind for 2028. Another interesting possibility not mentioned here is Tulsi Gabbard, who has been the subject of a lot of speculation but who has not been mentioned as a candidate by Trump himself.

The former president has said that he will likely announce his choice at the GOP's convention next month. If that holds, in a little over a month, we'll know — and after the convention, it's off to the races.