Dem
50
GOP
50
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.
Most observers think the Republicans are likely to capture the Senate. It is by no means a sure thing, especially if Democrats can win at least one of Florida, Montana, or Texas, or if independent Dan Osborn can win in Nebraska, but the polls seem to favor the Republicans.
The House is completely different. There are 17 districts that Joe Biden won in 2020 that have a Republican representative. All of these are in danger. To make it worse, a majority of them are in California and New York, where anti-Trump turnout is likely to be very high (and see below). Democrats need only to flip four seats to capture the chamber, assuming they can hold all of their own seats. There is a very realistic chance of the Democrats picking up the net four seats they need.
Of course, if both chambers flip, we will have divided government for at least 2 years and nothing will get done. Certainly nothing new there. (V)