Utah Sen. Mitt Romney (R) says it's "very likely" that he will side with Congressional Democrats over calling witnesses in the Senate impeachment trial against President Trump - however he says he will table the decision until Trump's defense team has concluded their opening arguments.

"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 said Saturday following the first full day of Trump's team's arguments, according to CNN.

The Utah Senator was mum on whether he thought Trump's team was effective, saying "I just don't have any comments on the process or the evidence until the trial is over."

Three weeks ago Romney expressed interest in hearing testimony from former National Security Adviser John Bolton, saying earlier this month "I would like to hear from John Bolton and other witnesses, but at the same time I'm comfortable with the Clinton impeachment model when we have opening arguments first and then we have a vote on whether to have witnesses."

Democrats need four Republicans to vote with them in favor of subpoenas for witnesses or new evidence in order to extend the trial and gather new information. There are only maybe four, realistically, who would vote in favor of calling witnesses who could testify against the President. That short list includes Romney, relative moderates Sens. Susan Collins of Maine and Lisa Murkowski of Alaska, and endangered senators up for reelection like Sen. Cory Gardner of Colorado. Collins and Murkowski have also signaled that they're open to hearing from witnesses, should they feel it's needed after opening arguments. -CNN

According to the report, Senate Majority Leader Mitch McConnell has blocked efforts by Democrats to push for an initial deal on witnesses and documents until after opening statements and questioning.

McConnell now says that calling witnesses would raise constitutional concerns - suggesting that he's in lockstep with Sen. Lindsey Graham (R-SC), who says "this needs to end."