Sen. Mitt Romney has indicated he will probably support the push from Democrats to call additional witnesses to testify in President Trump's Senate impeachment trial.

"I think it's very likely I'll be in favor of witnesses, but I haven't made a decision finally yet, and I won't until the testimony is completed," Romney told reporters Saturday.

Romney is one of a handful of key Republican senators that House impeachment managers are seeking to convince to allow more documents and witnesses as evidence in the trial. Chief among these is the testimony of John Bolton, Trump's former national security adviser. Democrats believe Bolton knows more about Trump's effort to pressure Ukraine to investigate the president's political rival, Joe Biden.

Romney's comments echoed similar remarks he made earlier this month when he said: "I would like to be able to hear from John Bolton. What the process is to make that happen, I don’t have an answer for you."

A House impeachment investigation found that a slew of Trump associates waged a campaign of shadow diplomacy in Ukraine while vital military aid and a White House visit were temporarily withheld from the war-torn country. During a July 25, 2019, phone call, Trump asked the president of Ukraine to "do us a favor" and investigate corruption allegations against Biden.

Bolton, according to people in the room that day, is said to have referred to this scheme as a "drug deal" that he wanted no part in. He resigned weeks later.

Trump, Democrats have argued, abused his power in orchestrating the pressure campaign against Ukraine. Romney, a frequent Trump critic, was the first Republican senator to signal his openness to hearing testimony from Bolton about the Ukraine scandal. The Utah senator called a transcript of the July 25 call "troubling in the extreme." A morning consult poll last week found him on shaky ground within Utah's Republican party.

House impeachment managers spent three days laying out the case against Trump and pleading with moderate Republicans such as Romney, Susan Collins of Maine, and Lamar Alexander of Tennessee to insist that Majority Leader Mitch McConnell allow additional witness testimony.

McConnell has said his position on impeachment and witness testimony will be in lockstep with the White House. He has dismissed the charges against Trump as "flimsy" and leading to a "slapdash" impeachment.

The president's defense team began its first day of opening arguments by attacking the credibility of House impeachment managers.

“Impeachment shouldn’t be a shell game,” Pat Cipollone, one of Trump's impeachment lawyers, told senators on Saturday.

Trump has for months complained that his impeachment is a total "sham" that is inspired by a deep hatred for him among "crazy" Democrats.

