Washington (CNN)Maine Republican Sen. Susan Collins said she won't endorse GOP presumptive presidential nominee Donald Trump until he starts behaving more "presidential." "I would love to be able to endorse Donald Trump, but he really has to change the approach that he's taken," she told CNN's Chris Cuomo on Wednesday on "New Day." "If I were giving him advice, I would tell him he should own up to making mistakes. He should apologize to the judge and to the American people. And he should stop insulting people."