“We are obviously discussing — assuming this comes over to us — what the different options and so forth are and how to prepare for some of those various and potential contingencies, " Senate Majority Whip John Thune (R-S.D.) said, declining to comment specifically on the GOP leader's remarks.

McConnell's warning comes as the House on Wednesday opened public hearings in its impeachment inquiry, marking the next phase of the historic proceedings.

The Kentucky senator added that it’s “impossible to predict” how long an impeachment trial in the Senate would last and said it's up to senators. He noted President Bill Clinton's impeachment trial was a "totally different case."

McConnell and Minority Leader Chuck Schumer have yet to decide how the Senate will handle an impeachment trial. The New York Democrat told reporters Wednesday it is “premature” to discuss the trial’s length, noting the House will need to act first.

“We want it open and we don’t want it truncated,” Schumer said. “We hope that Leader McConnell would negotiate in a fair, balanced way with us.”

McConnell and Schumer will at some point need to agree on the terms of an impeachment trial, including types of amendments or witnesses to bring up. Some Senate Republicans have suggested Hunter Biden, former Vice President Joe Biden's son, should come and testify and theoretically could do so under Senate rules.

Republicans have criticized Hunter Biden for his work for Burisma, a Ukrainian gas company, while his father was working on anti-corruption efforts as vice president.

Burgess Everett contributed to this report.