The first congressional election was in 1788. In the 118 federal elections since then, it has never happened that partisan control of the Senate and House flipped in opposite directions in the same election. Not when the Federalists were around, not when the Whigs were around, not ever. This year there is a realistic chance that it could happen, because the dynamics of the Senate and House are so different, with the entire House up but only 34 seats in the Senate, the majority of which are in blue states.