Sen. Tom Cotton praised President Donald Trump's selection of John Bolton as national security adviser as an "excellent choice to take the baton."
"H.R. McMaster is a warrior and a scholar, one of the best generals of his generation," the Arkansas Republican, who sits on the Senate Armed Services Committee, said in a statement.
"I join all Arkansans in thanking him for decades of service to our nation, most recently as President Trump's national security adviser."
Trump tweeted Thursday that Bolton, 69, the former United Nations ambassador, would take over the post on April 9.
McMaster, 55, a three-star Army lieutenant general who remains on active duty, said he would "leave public service" this summer after retiring from the military.
"I also congratulate Ambassador John Bolton for his appointment as the next national security adviser," Cotton said. "He's an excellent choice to take the baton from Gen. McMaster."