1. Democrats have a razor-thin margin in the House of Representatives: only four seats. The Senate map in 2022 favors Democrats somewhat, and there's a chance their margin in the Senate could increase, but in this hyperpartisan era, a party needs to hold both houses of Congress in order to get anything done there.
2. Midterm elections generally go against the party in the White House, because those who oppose that party are more motivated to resist it than those who support it are to increase its margin. Satisfied people stay home. The only recent exceptions are 1998 and 2002, both driven by unusual events (one by the Lewinsky-scandal impeachment and the other by the rally-round-the-flag effect in the wake of September 11) and both in a less polarized atmosphere than we have today.
3. The resistance to COVID precautions has caught Biden in a double bind. People want to "get back to normal", and many are liable to blame the incumbent president if they can't, but living like it's 2019, or anything even close to it, is impossible as long as COVID is still circulating at current levels. The biggest reason it keeps circulating like this is the large population who refuse precautions, most egregiously those who refuse vaccination. Biden doesn't have the authority to force them to get vaccinated and wear masks, and when he uses the powers he does have, such as mandating that all employees of federal contractors get vaccinated, the resisters scream bloody murder. Therefore, he gets blamed no matter what he does.
4. Presidents receive credit or blame for the economy far out of proportion to the degree of control they actually have. The economy is actually experiencing an employment boom, but media coverage emphasizes the inflation more.
5. Gerrymandering can be carried out with unprecedented scientific precision these days, and Republicans have weaponized it to a greater degree than Democrats. Of the
seven states that have nonpartisan redistricting commissions, four are blue (including the whale that is California), two are swing, and only one is red. So Republicans have a built-in advantage in the House.