Polls and US pundits seem to agree that the "red wave" signaled by earlier polls was decisively thwarted by 2 factors:
(1) Republicans gravely underestimated how high a voting priority for most Americans it was for abortion to remain legal. The demise of Roe v. Wade was not the main issue: the main issue was the simplistic Republican stress on a pro-life agenda, which lacked the political savvy to recognize that their real focus should have been on the number of weeks abortion should be legal. Most American support such limits; so that could have been a winning issue.
(2) The vast number of Republican election deniers and their tepid response to the January 6 insurrection painted the Republican party as the party of extremists in the eyes of swing voters who might otherwise have voted Republican. Sadly, at this state of American politics, hatred of "the other party" is more significant than the party that most agrees with one's issues. I have no hope that the expected Republican House will be willing to cooperate with a Democrat Senate to get anything important done. Remember, the House controls the purse strings.
Trump set the extremist tone on these 2 issues. If his imminent "big announcement" is that he will run for president in 2024, Republicans will lose the next presidential election, despite Biden's abysmal approval ratings, unless other more viable Republican presidential candidates emerge: e. g. Ron DeSantis, Nike Pence, Nicki Haley, and Kristi Noem. But I fear that they can't beat Trump in a presidential primary and that most of them might see this as a reason not to run. Yet there is hope: my Republican friends are already receiving calls to donate to an anticipated DeSantis presidential campaign.