Vice President Kamala Harris said on Wednesday that former President Donald J. Trump’s reported comments praising Nazi generals offered “a window into who Donald Trump really is,” calling it “deeply troubling” that her Republican rival had apparently invoked Hitler in conversations with one of his former chiefs of staff, John F. Kelly.

Ms. Harris and her campaign have pounced on Mr. Kelly’s comments, recounted in recent news stories and in on-the-record interviews, in the hopes that she will benefit with undecided voters and a slice of conservative-leaning ones by refreshing their memories of a Trump presidency 13 days before Election Day.

In her brief remarks, delivered at the vice president’s residency in Washington, Ms. Harris warned that Mr. Trump had grown “increasingly unhinged and unstable” and said that he would require that the U.S. military “be loyal to him personally,” even if Mr. Trump did not obey the law during the course of a second term.