Donald Trump, as the potential Republican nominee for president, narrowed his list of possible vice presidential candidates in early May. After shuffling dozens of names and making a cost-benefit calculation for each, he narrowed the lineup to four names: Marco Rubio, JD Vance, Tim Scott and Doug Burgum. He recently went a step further, and his campaign team contacted them to investigate their backgrounds.

As Bloomberg reported at the time, the Florida senator, the Senator from Ohio, the Senator from South Carolina, and the governor of North Dakota are the four finalists to be Trump’s running mate. Trump currently leads the Democratic president in many key states.

Now, according to The Hill, and based on a source from the Republican’s campaign, the magnate’s staff went one step further and asked the candidates for a background investigation.

On the other hand, while it is unclear if it is to evaluate a possible vice presidential run, ABC News reported that Elise Stefanik, Byron Donalds and Ben Carson also received similar requests, although it is unclear how extensive. The members of Congress and the former Secretary of Housing and Urban Development have also been under consideration by Trump in the past.

However, Rubio, Vance, Scott and Burgum remain the favorites in this race, which Mike Pence won in 2016. Indeed, each reacted to the decision of the Manhattan jury backed by Trump, who even praised them each in a recent interview with Newsmax.

“I thought Tim Scott didn’t run as good a race as he’s capable of running on his own, but as a substitute for me, he’s incredible. He has been incredible,” said the tycoon.

“Governor Burgum of North Dakota has been incredible. Marco Rubio has been great. JD Vance has been fantastic. We have had so many wonderful people out there,” he added.

As a curious fact, all four names have criticized the magnate in the past, some more harshly than others. Rubio even faced him directly in the 2016 presidential elections when he came third in number of delegates.

Trump is expected to announce his decision weeks before the Republican National Convention (RNC), which will take place between July 15 and 18.