Sen. Robert F. Kennedy is held by an aide as he stands on a car seat while campaigning in Sacramento, Calif. in this May 16, 1968 photo. President Johnson's loss to Sen. Eugene McCarthy demonstrated his vulnerabilty and soon Sen. Kennedy joined the quest for the democratic presidential nomination. The hallmark of the New Hampshire primary -candidates meeting voters face-to-face, answering their tough questions one-on-one - began in 1952 with another challenge to a sitting president. Until then, the names of delegates rather than candidates appeared on primary ballots. (AP Photo)