Frustration spilled out on the Senate floor Saturday morning as Sen. Ron Johnson got into a heated conversation with Sen. Mitt Romney, as the Utah senator voted to allow witnesses at former President Donald Trump's impeachment trial.

Johnson, R-Wis., turned to Romney in the Senate chamber during the vote visibly upset and even pointed a finger at Romney.

The two Republicans were exchanging words back and forth as fellow GOP Sen. Dan Sullivan of Alaska acted as a buffer between them.  

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Johnson was overheard by a Fox News reporter in the Senate chamber telling Romney, "blame you." Their voices were raised. 

Sen. Mitt Romney, R-Utah, and Sen. Ron Johnson, R-Wis., got into a dustup Saturday during a Senate impeachment vote on allowing witness testimony. (Reuters/FOX)

Romney was one of five Republicans to join Democrats in a 55-45 vote to extend the trial by subpoenaing witnesses to testify. The others were Sens. Susan Collins of Maine, Lisa Murkowski of Alaska, Ben Sasse of Nebraska and Lindsey Graham of South Carolina, who changed his vote in the final minutes. 

Johnson declined to discuss the details of his "private" conversation with Romney to pool reporters afterward. When told that reporters overheard his dustup all the way from the balcony and just wanted clarification, Johnson said: "That’s grotesque you guys are recording us." 

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Johnson later told Fox News that he wasn't upset with Romney but with the outcome of the vote to allow witnesses.

"I was upset at the vote," Johnson told Fox News.

Romney also declined to discuss the details of his conversation with Johnson and quipped to reporters: "We were arguing about boxers vs. briefs"

Romney was the only Republican to vote to convict Trump in his first impeachment trial. During the second impeachment, for incitement for insurrection, he's voted with Democrats on key procedural moves to declare the trial constitutional and to allow witness testimony.

Fox News' Kelly Phares contributed to this report.