Cook Political Report published an analysis piece today titled “How Big Is the House Playing Field?” The piece starts from an acknowledgement that the midterms are shaping up as very bad news for Democrats.

This week, Democratic and Republican campaign operations acknowledged that the House playing field is expanding. The NRCC added another 10 House districts to its already robust list of 72 Democratic-held targets. And on the Democratic side, the House Majority PAC announced it would be reserving nearly $102 million in advertising in a whopping 51 media markets for the fall campaign.

These moves suggest that both sides see the possibility of a Red Tsunami in 2022.

But the main thrust of the piece is that there are factors that could restrain a Red Tsunami to something slightly less dramatic. Looking the GOP’s advantage in the generic congressional ballot (currently +3.6 at RCP), Cook predicts about a 7 point shift toward the GOP, meaning any district where Biden won by less than 7 would be in danger. The good news for Dems is that there aren’t that many of those:

…there are only 21 districts where Biden’s margin was fewer than seven points. Even if we expand that universe to include districts Biden carried by 8-10 points, that universe of potentially vulnerable Democratic-held seats expands only slightly…

Every metric we use to analyze the political environment — the president’s approval rating, the mood of the electorate, the enthusiasm gap — all point to huge gains for the GOP this fall. But, those metrics are bumping up against an increasingly ‘sorted’ House with few marginal seats and few incumbents sitting in the “wrong district.” As such, the more likely scenario for this fall is a GOP gain in the 15-25 seat range.

Twenty-five House seats would be a big shift but it sounds small compared to the 54 seats the GOP gained in 1994. But don’t forget that Democrats lost 13 seats in 2020 even as Biden won the White House. So a further shift of 25 would represent a gain of nearly 40 over two election cycles.

The other key reason this year’s shift may not be as big as previous ones is redistricting. Five Thirty Eight has a piece about this which explains that the House will now be more balanced than it has been in a while, largely because Democrats succeeded in gerrymandering districts in states like New York.

As the maps stand on March 30 at 5 p.m. Eastern, 175 congressional districts have a FiveThirtyEight partisan lean1 of D+5 or bluer, 181 have a partisan lean of R+5 or redder and 33 are in the “highly competitive” category between D+5 and R+5.

That’s a net increase of 11 Democratic-leaning seats from the old maps. Meanwhile, the number of Republican-leaning seats has decreased by six, as has the number of highly competitive seats.

The fact that there are far fewer “highly competitive” seats than their used to be is another reason that even a 7 point shift toward the GOP won’t result in the kind of gains we saw in 1994. Here’s a graph from Five Thirty Eight showing the change over time:

BTW, the reason the excerpt above says there are 33 highly competitive seats while the graph shows 41 is that the graph includes a best guess for 4 states that have not yet completed redistricting, Florida, Maryland, Missouri and New Hampshire. The range for the final outcome is 36 to 42 highly competitive seats so 41 is near the top of that range. In any case, there will be a lot fewer of them this year then there were in the 90s, so the potential shift based on a 7 point swing is also a lot smaller.

Of course even with a 15 seat shift, the GOP would take control of the House and that’s really the end of passing any portion of Biden’s agenda for the rest of his term. That’s not much of a best case scenario.