In 1955, Johnson persuaded Oregon's Independent Wayne Morse to join the Democratic caucus.[66]
A 60-cigarette-per-day smoker, Johnson suffered a near-fatal heart attack on July 2, 1955, at age 46. He abruptly gave up smoking as a result and, with only a couple of exceptions, did not resume the habit until after he left the White House on January 20, 1969. Johnson announced he would remain as his party's leader in the Senate on New Year's Eve 1955, his doctors reporting he had made "a most satisfactory recovery" since his heart attack five months before.[67][68]

Campaigns of 1960
See also: 1960 United States presidential election
Johnson's success in the Senate rendered him a potential Democratic presidential candidate; he had been the "favorite son" candidate of the Texas delegation at the Party's national convention in 1956, and appeared to be in a strong position to run for the 1960 nomination. Jim Rowe repeatedly urged Johnson to launch a campaign in early 1959, but Johnson thought it better to wait, thinking that John Kennedy's efforts would create a division in the ranks which could then be exploited. 