WASHINGTON – The Donald Trump campaign has stepped up its vice presidential search, requesting detailed information from at least four of the top contenders.

North Dakota Gov. Doug Burgum, Florida Sen. Marco Rubio, Ohio Sen. J.D. Vance, and South Carolina Sen. Tim Scott have all been asked to submit background information to the Trump campaign, according to two people familiar with the process.

Trump cited those four names in an interview on Tuesday with Newsmax. The presumptive Republican nominee said he would probably hold off on an official announcement until the Republican convention July 15-18 in Milwaukee.

“We’ve had so many great people out there,” Trump said in the interview.

Sources cautioned the situation is fluid and could always change, given Trump’s mercurial nature.

The campaign has increased activity on the running mate front now that his hush money trial is over.

A New York jury convicted Trump of falsifying business records in order to hide hush money payments to an adult film star from voters, all in an effort to influence the 2016 election.

The candidates under consideration have not commented on their prospects to be Trump’s running mate.

Trump and his aides have discussed a number of other possible running mates, including Rep. Elise Stefanik of New York, Rep. Byron Donalds of Florida, and former housing secretary Ben Carson.

One other name has been discouraged by Trump: Former South Carolina Gov. Nikki Haley, a fierce primary rival of the former president.

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Trump said on Newsmax: “As far as Nikki’s concerned, I was very disappointed in her because she stayed too long.”