Washington (CNN) Republican Georgia Sen. Kelly Loeffler targeted her colleague GOP Sen. Mitt Romney of Utah on Monday over the issue of witnesses at the Senate impeachment trial.

In a tweet, Loeffler leveled an accusation at Romney, saying, "After 2 weeks, it's clear that Democrats have no case for impeachment. Sadly, my colleague @SenatorRomney wants to appease the left by calling witnesses who will slander the @realDonaldTrump during their 15 minutes of fame. The circus is over. It's time to move on!"

Loeffler, a political novice and businesswoman, was sworn in as Georgia's newest senator earlier this month, taking over the seat previously held by then-Sen. Johnny Isakson, a Republican who retired at the end of last year over health concerns.

Her comments about Romney come as a debate over whether there should be witnesses called during the trial has intensified in the wake of a New York Times report that former national security adviser John Bolton's draft manuscript says President Donald Trump told him US security assistance to Ukraine was conditioned on investigations into Democrats, including former Vice President Joe Biden.

CNN has reached out to Romney's US Senate office with a request for comment, but has not yet received a response on the tweet from Loeffler.

Loeffler and her husband donated "a combined $1.5 million to pro-Romney super PAC Restore Our Future to boost his unsuccessful 2012 presidential bid," according to the Center for Responsive Politics . Federal Election Commission records show that Loeffler also donated to Romney's 2012 presidential campaign.

Romney, an occasional critic of the President, has not definitively said that he plans to vote for a subpoena for Bolton's testimony, but he has indicated that he would like to hear from Bolton.

Last week, Romney said , "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." On Monday, he said that he believes it is "increasingly likely that other Republicans will join those of us who think we should hear from John Bolton," in the wake of the report.

Romney has been careful not to tip his hand during the impeachment trial on how he plans to ultimately vote on whether to convict or acquit, and frequently tells reporters that he does not plan to comment extensively on the proceedings until the end of the trial.

In 2013, Atlanta Magazine interviewed Loeffler and her husband and asked them about their contributions to Romney.

Loeffler's husband, Jeff Sprecher, told the magazine, "We met Mitt Romney and got to know him personally many, many years ago, when he was trying to run in the primaries against John McCain ... We got to know him and his wife, and have been to his house many times and they've been to our house. Taking politics off the table, the Romneys are really lovely people, and well intended ... And so it was easy to support a friend."

The President's legal team is currently presenting arguments in defense of the President during the trial after the House impeachment managers presented their arguments last week. Once the defense team arguments conclude, senators will have a chance to ask questions of both the President's legal team and the House managers who are acting as prosecutors.

Democrats have ratcheted up their calls on Republican senators to vote to hear from witnesses in response to the Times report, but a number of GOP senators, including members of Republican Senate leadership, downplayed the report related to Bolton on Monday.

Sens. Lisa Murkowski of Alaska and Susan Collins of Maine, two other Republican senators who have been closely watched during the trial for how they might vote on the question of witnesses, also commented on the report Monday.

Collins said Monday morning that "the reporting on John Bolton strengthens the case for witnesses and has prompted a number of conversations among my colleagues."

Murkowski made her own statement Monday, saying, "I stated before that I was curious as to what John Bolton might have to say.

"From the outset, I've worked to ensure this trial would be fair and that members would have the opportunity to weigh in after its initial phase to determine if we need more information," Murkowski said. "I've also said there is an appropriate time for us to evaluate whether we need additional information -- that time is almost here. I look forward to the White House wrapping up presentation of its case."

This story has been updated with additional developments Monday.