WASHINGTON — Senator Lisa Murkowski of Alaska expressed unease in an interview broadcast on Tuesday with the Senate majority leader’s vow of “total coordination” with the White House on impeachment proceedings against President Trump, a potentially significant crack in Republican unity.

Ms. Murkowski, a moderate with an independent streak, told Anchorage’s NBC affiliate KTUU she opposed “being hand in glove with the defense” and voiced other concerns as the Senate prepares to hold a trial over the two articles of impeachment that the House approved earlier this month.

Ms. Murkowski’s views could prove important. She rarely speaks publicly against Republican leadership, but when she does, she tends to stick with her positions, as when she opposed the confirmation of Justice Brett M. Kavanaugh and helped torpedo a repeal of the Affordable Care Act. She also tends to bring Senator Susan Collins of Maine, a fellow moderate Republican with her. Only a handful of defections would force the majority leader, Senator Mitch McConnell of Kentucky, to switch course on the upcoming impeachment trial.

In the interview, Ms. Murkowski said she was “disturbed” by comments by Mr. McConnell that indicated he intends to work in concert with the White House counsel in planning the impeachment trial.