We don’t want Hillary back on the ticket at the last minute.
Scenario:
1) Obama wins the election.
2) Obama is severely implicated in multi-state RICO investigation.
3) The specter of Obama being impeached a few months into his Presidency rises.
4) Hillary Clinton begins quietly lobbying Democratic electors to vote for her
5) Enough Democrat electors vote for Hillary that there is no college majority.
6) The election goes to the House of Representatives.
7) Obama’s stock has plummeted and after numerous rounds, the House elects Hillary Clinton POTUS.