It could all come down to 17 crucial days in January.

If Democrats win back the Senate and lose the White House in November, they would control both branches of government for about two weeks before Obama leaves office. That overlap in the transition of power is set in stone. The Constitution mandates the new Congress begins work on January 3, while President Obama stays in power until January 20.

So if Democrats take back the Senate, President Obama could send a Supreme Court nominee to that new Democratic majority, which would have 17 days to change the filibuster rules and ram in a vote before a new President takes power.

“If a Democratic Senate comes in on January third, President Obama could send in his Supreme Court nomination,” explained a former Obama administration lawyer. “Then Democrats could apply the ‘nuclear option’ to Supreme Court nominations, and vote in Obama’s nominee by a simple majority.”