[139] Kennedy was himself undecided about the position and, knowing that the prospect rankled Johnson, was content to eliminate himself from consideration. Ultimately, Goldwater's poor polling numbers degraded any dependence Johnson might have had on Kennedy as his running mate.[140] Hubert Humphrey's selection as vice president then became a foregone conclusion and was thought to strengthen Johnson in the Midwest and industrial Northeast.[141] Johnson, knowing full well the degree of frustration inherent in the office of vice president, put Humphrey through a gauntlet of interviews to guarantee his absolute loyalty and having made the decision, he kept the announcement from the press until the last moment to maximize media speculation and coverage.[142]
In preparation for the Democratic convention, Johnson requested the FBI send a squad of thirty agents to cover convention activities; the objective of the squad was to inform the White House staff of any disruptive activities on the floor. The squad's focus narrowed upon the Mississippi Freedom Democratic Party (MFDP) delegation, which sought to displace the white segregationist delegation regularly selected in the state. 