Wallace does well enough to throw the election to the House in 1968, and Kennedy survives against a divided GOP's Rockefeller in 1972 (a disaffected conservative like James Buckley or maybe Activist Jesse Helms runs third-party). By 1976, Democrats' luck runs out with the Fall of Saigon, Oil Shock, and a sixteen-year itch. Vice President Sanford is diagnosed with a heart murmur as OTL but runs anyway. He's probably tempted to pick Los Angeles Mayor Tom Bradley as his running mate for a historic first, but is dissuaded to prevent a total wipeout. Some liberal Republicans object to Reagan and some conservatives are dissatisfied with Schweiker as running mate, but by then the party is too traumatized by third-party spoilers to split again.
Vice President Terry Sanford (D-NC) / Senator Adlai Stevenson (D-IL)
Fmr. Governor Ronald Reagan (R-CA) / Senator Richard Schweiker (R-PA) ✓