(WASHINGTON) -- 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.
"Anyone claiming to know who or when President Trump will choose his VP is lying, unless the person is named Donald J. Trump," said Brian Hughes, a senior adviser for the Trump campaign.
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.
While the former president hasn't yet indicated who he will pick to be his vice president, he has said he plans to make his announcement closer to the Republican National Convention, which is in July.
Over the past few weeks, those under consideration as a possible vice president for Trump have increased their public profile by appearing on cable networks, defending the former president during his hush-money trial and with some even making an appearance at court with Trump.
Burgum was the only known potential veepstakes contender to appear at the courthouse during jury deliberations for Trump's criminal trial, which happened only after Trump campaign representatives asked him to provide background information to be considered in the running-mate search.
Last week, following television appearances outside the courthouse, Burgum joined Trump and his son, Donald Trump Jr., as the jury deliberated. Two hours later, Trump was convicted.
Burgum's appearance signaled a sign of loyalty in the next initial steps and strength as a partner through tumultuous waters.
Vance also appeared as a surrogate at the courthouse in Manhattan on May 13.
Often asked about the possibility of serving as vice president under Trump, Burgum, Rubio and Vance have often deflected answering the question head-on, but have said they would do what the Trump campaign asked of them, which has included being campaign surrogates and raising money for the former president's campaign.
Discussions have taken place with the Rubio team about how to address the constitutional issue that may prevent residents from the same state from being on the same presidential ticket -- including the possibility of the Florida senator relocating for the role, sources said.
When recently asked on NBC if he wanted the job of vice president, Rubio said, "I'll do whatever the campaign asked me to do."
During a phone interview on Newsmax on Tuesday night, Trump was asked if he was close to making a decision on picking a running mate and complimented Vance, Rubio and Burgum.
"I thought Tim Scott didn't run as good of a race as he's capable of running for himself, but as a surrogate for me, he's unbelievable. He's been incredible," Trump said.
"Gov. Burgum from North Dakota has been incredible. Marco Rubio has been great. J.D. Vance has been great. We've had so many great people out there," he said.