By 1968, Warren was ready to retire from the Court. He hoped to travel the world with his wife, and he wanted to leave the bench before he suffered a mental decline, something that he perceived in both Hugo Black and William Douglas. He also feared that Nixon would win the 1968 presidential election and appoint a conservative successor if Warren left the Court later. On 13 June 1968, Warren submitted his letter of resignation to President Johnson (who made it official on 21 June), effective upon the confirmation of a successor. In an election year, confirmation of a successor was not assured; after Warren announced his retirement, about half of the Senate Republican caucus pledged to oppose any Supreme Court appointment prior to the election.