In 2015, Humphrey endorsed Ohio governor John Kasich for President in 2016. During the 2016 Republican presidential primaries, Humphrey was a leader of efforts to try to block Donald Trump from securing the nomination at the Republican National Convention. He stated, "I would only vote for Hillary [referring to Hillary Clinton, the Democratic nominee] in the event of a very close contest. Meantime, I'm hoping the Republican leadership, at long, long last will show the courage and principle to denounce Trump and to demand he renounce the nomination or face a reconvening of the convention." On November 6, 2016, two days before the election, Humphrey officially endorsed Clinton. That same month, Humphrey left the Republican Party and became an independent.