There seem to have been a lot of maps on here very unfavorable towards George McGovern. Nixon resigns in 1972. Agnew decides not to run for the presidency since the tax evasion news comes out then and the Republicans can't find a definitive candidate to run.
What happens?
There's no way the Republicans or Democrats would ever not run a candidate. This is not 1820. The Democrats had no chance in hell in 1920, 1924, 1972, and 1984 but still ran candidates, the parties are afraid that they will lose power