Bolton's offer to testify puts new pressure on Mitch McConnell -- and could prove damning to Trump
Senate Majority Leader Mitch McConnell (screengrab)

Former national security adviser John Bolton has announced he would be willing to testify at President Donald Trump’s impeachment trial if the Senate issued him a subpoena.

Bolton declined to say what he would tell the Senate about Trump's pressure campaign against Ukraine, but former White House officials and sources close to Bolton said the testimony could be damning and put new pressure on GOP senators to convict him, reported the New York Times.

Democrats have demanded additional testimony from aides blocked by the White House from appearing before the House impeachment inquiry, and Speaker Nancy Pelosi has refused to send over the articles of impeachment until Senate Majority Leader Mitch McConnell agrees to hold a fair trial.

Bolton's announcement puts additional pressure on McConnell to call witnesses at the trial instead of rushing it through to protect the president.

It's not clear how the White House will respond, but Bolton's statement indicates he would testify even if Trump objected.