In 1967, he was asked to run for the House again in the 1968 election, but chose not to. During the 1968 Democratic presidential primaries he supported Senator Robert F. Kennedy and was a member of his staff. When Roncalio heard about Robert Kennedy's assassination he stated that "I can't think of anything appropriate newsworthy or decent to say". After Kennedy's death he supported the anti-Humphrey movement at the national convention. In April 1969, William A. Norris Jr., Wyoming's Democratic national committeeman, announced that he would resign and on May 5, 1969, Roncalio was selected to replace him by acclamation after Joe Stewart, the only other candidate, withdrew two days before.