Trouble for piloted flybys

1964-67: Expanding war in Indochina; cost reaches $25 billion/year; growing federal deficit
July 1965: Mariner 4 performs successful Mars flyby, showing that astronauts are not required for flybys
January 1967: Apollo 1 fire undermines confidence in NASA; Congress unwilling to fund post-Apollo programs
February 1967: President's Science Advisory Council criticizes PF concept