Washington (CNN) The White House has been involved in discussions with GOP allies over the last several days to make sure they're ready in the event Democrats get enough votes to allow witnesses, such as former national security adviser John Bolton, to testify in President Donald Trump's impeachment trial, a senior administration official and a person familiar with the matter tell CNN.

The sources say part of those discussions involve the implications, such as executive privilege concerns, if former and current White House officials such as Bolton and acting White House chief of staff Mick Mulvaney are forced to publicly testify.

Testimony from those officials could add key revelations to the inquiry because of their first-hand knowledge of the administration's dealings with Ukraine.

"There are a series of contingencies. We're prepared," the senior administration official said. The sources would not disclose what the contingencies are.

Senate Minority Leader Chuck Schumer and Senate Democrats have pushed for the Senate to hear from four witnesses, including Bolton and Mulvaney, and to subpoena documents that the White House blocked from the House's impeachment inquiry. But Senate Majority Leader Mitch McConnell says he has enough Republican votes to back the rules resolution without Democratic support.

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