Mitt Romney says it's 'increasingly likely' GOP senators will call for John Bolton's testimony

• It's "increasingly likely" GOP senators will call for John Bolton to testify, Sen. Mitt Romney told reporters on Monday.
• This came after it was reported Bolton in an upcoming book undercut one of President Donald Trump's key defenses against impeachment.
• Bolton reportedly wrote that Trump explicitly told him he was withholding military aid from Ukraine in exchange for investigations he wanted into political rivals, including former Vice President Joe Biden.
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GOP Sen. Mitt Romney of Utah on Monday said it's "increasingly" important that the Senate hear from former national security adviser John Bolton in the impeachment trial and therefore "increasingly likely" he'll be called to testify.

"It's increasingly apparent that it would be important to hear from John Bolton," Romney told reporters. "I, of course, will make a final decision on witnesses after we've heard from heard from not only the prosecution but also the defense. But I think at this stage it's pretty fair to say that John Bolton has a relevant testimony."

"It's increasingly likely that other Republicans will join those of us who think we should hear from John Bolton," Romney added.

This came after a report emerged Sunday night about Bolton's forthcoming book, in which the former adviser wrote that Trump in August told him he wanted to continue a freeze on roughly $400 million in military aid to Ukraine until investigations were launched into Democrats, including former Vice President Joe Biden.

Trump was impeached in December for abuse of power over his dealings with Ukraine and obstruction of Congress in relation to his efforts to stonewall the impeachment inquiry. The president has been accused of withholding military aid from Ukraine as he sought to pressure it into announcing investigations that would have been advantageous to his 2020 reelection campaign.

Bolton's book could undermine one of the key defenses from Trump and his legal team: that there was no quid pro quo, or no explicit link between the military assistance and request for investigations.

Democrats for weeks have been pointing to Bolton as a vital witness, given mutiple other witnesses have testified he was extraordinarily concerned about the Trump administration's efforts to pressure Ukraine.

Republicans have pushed against calling for witnesses, however, accusing Democrats of rushing the process instead of taking time to gather sufficient evidence. But the Trump administration refused to comply with subpoenas or allow witnesses to testify in the impeachment inquiry, and there's been much speculation in Washington as to whether Trump will invoke executive privilege in an attempt to stop Bolton from testifying.