The question of who controls the Senate may get a little trickier after the November election as the odds of a 50-50 split in the chamber look increasingly likely.

To flip the Senate, Democrats need a net gain of three or four seats, depending on whether President Trump and Vice President Mike Pence win a second term, or presumptive Democratic nominee and his soon-to-be-announced running mate occupy the West Wing. The vice president breaks ties on Senate votes and may be needed a fair amount.