Congressional Elections - Senate: Those who foresee a difficult year for Democrats' chances to hold onto the majority in the Senate are correct. Not quite impossible but unlikely. This is true in most Presidential political scenarios.
As with the Presidential election, there are only a few states where the race should be close, and those are mostly Democratic-held. West Virginia's seat was already lost before Joe Manchin decided not to run for re-election, and that brings the prospective count to 50-50, before considering the tough, but winnable re-election races. The other shaky Democratic Senate vote, former Democrat Krysten Sinema's Arizona one, may end up being good news, as Sinema's running third in a three-way race, with Democratic Congressman Ruben Gallego now slightly favored to win it over Trumpist Kari Lake. .
Other holds may be more difficult. Top of the list is Jon Tester in heavily Republican Montana, though he has successfully defended it in the past and will likely face an extremist. The same challenge, only in a larger, more expensive state, faces Sherrod Brown in Ohio, but he has the same strong record in statewide elections. Tammy Baldwin has done well in the past in Wisconsin, but the state's electoral balance is narrow--she might be in danger if the Republicans nominate someone even a bit more moderate than their other senator, Ron Johnson. Michigan's seat is now a toss-up since Debbie Stabenow decided not to run again, and it looks to be a battleground in the Presidential race, once again. Jacky Rosen needs to defend her seat in Nevada, and that state's votes are always close.
There are 10 or more seats on each side that seem very secure: the likes of NY ,CA, WA, and the New England states for the Democrats; and several Midwest and South states for the Republicans. There are several states in between--clear favorites but not slam-dunk landslides. I'd include in that set PA, where Bob Casey should run well ahead of the Democratic Presidential nominee; a few Midwest states with strong Republican majorities but have challengers who could surprise (MO, NE, ND); Florida and Texas, which have controversial and unpopular Republican incumbents (Rick Scott and Ted Cruz) but definite Republican leans; and New Mexico and Maine, with reasonably strong Democratic tendencies and popular incumbents.
I should mention New Jersey's Democratic Senator, Bob Menendez, who is facing a second criminal charge (along with his wife), one that looks devastatingly bad based on large chunks of presumed bribe money found in his house. One more stress-inducer for Chris Van Hollen, the Democratic Senate campaign head. He's certainly hoping Menendez will be successfully primaried, but it may not happen that way (dare I suggest Jersey folks have a high tolerance for corruption, especially for people of their party?), which would make the general election very risky. If he's primaried out, it becomes a likely Democratic hold.
Incumbent Senators running for re-election do tend to win in most general elections, but Presidential landslides or very unpopular administrations can upset this. We should not exclude that possibility, either that the Democrats hold on to their majority or even grow it if Trump fades, or that a big Republican night takes them to 53-55 seats from their current 49.
Congressional Elections: House - Despite the parties' efforts to make the House seats they hold as safe as possible, there are many unknowns about the House of Representatives and who may control it after 2024. One manifestation of this is the great number of Representatives choosing not to run again, though that does not in itself indicate the winner, as they are numerous from both parties. The majority of those seats thus opening up are deemed safe within party, but those are the type that could flip if the Presidential race tilts heavily to one side.
Meanwhile, there are a couple dozen that are held by Representatives from the party that was a minority in the last Presidential election (as projected with new Congressional boundaries). This may prove to be an indicator of seats that will change hands; if so, this favors the Democrats to gain the (two? four? five?) seats they will need to gain on Election Day to gain control of the House. \
Redistricting--in this case, also known as gerrymandering--could play a role in how control of the House plays out, and at this point provides additional uncertainty. The Supreme Court has given state legislatures somewhat of a free hand in rejiggering Congressional district boundaries for partisan advantage, and they are taking advantage of it, in North Carolina (to favor Republicans) and New York (to favor Democrats). There are also a couple of states in the deep South where the courts have ruled that district boundaries must be changed to create one or two more majority-nonwhite districts. The state legislatures are not aligned with that order, so far. As the deadlines approach, these issues will get resolved in the courts (basically, any change result will be challenged by the side perceiving disadvantage); some seats will change hands ultimately as a result, but again, that might net out to little to no advantage to either side vs. 2022.
Congressional Control: At this distance of 50,000 feet and 10+ months, the most likely outcome, barring the scenarios where Trump or Biden fades or drops out, is an unusual one, with control of both Houses changing, the Senate to Republicans and the House to Democrats.
The former is a probability based on the numbers: the Democrats have many seats at risk, and the Republicans few to none. The Democrats will likely save many or most of them, but after losing Manchin's seat, they can afford no net loss.
As for the House, I expect there will be strong turnout in 2024, which will tend to favor Democrats. I expect in particular a gain of five seats or so just from NY and CA. That would be enough, but if the Democrats repeat the clear Presidential popular vote majority they had in 2020 (7 million votes), gerrymandering won't be enough to stop it, and the margin could be larger than the 222-213 result we saw in the last two Congressional elections.
State Legislatures/Gubernatorial Races - I won't go too deep, but it's clear these electoral contests are only becoming more important in the general partisan context, particular as it relates to setting rules for Federal elections. So more money than ever will be spent.
A few general comments at this point: Somewhat surprisingly, gubernatorial elections don't necessarily follow the pattern of Federal elections, especially not the Presidential outcomes. There are plenty of blue state Republican governors, some red state Democratic ones, and swing state governors of both types. And even independents can win statewide. Gaps between contested governors' races vs. Presidential ones can be 10-15 percent. So those need to be viewed independently of the Presidential contest, the results of which are almost baked in for most states.
There will be a serious effort by the Democratic party to try to take control of more state legislatures in 2024. The party's campaign committee created specifically to fund strategic races has low recognition and is chronically underfunded, but this year I think legislative races will get more assistance from above. This will correct a glaring political strategic error the Democratic party has been committing since Obama's time.
State races may produce an upstream effect on the Presidential race through special turnout efforts. Major voter registration efforts can make a difference. Ballot measures are another difference-maker; Democrats will seek to have abortion and/or cannabis initiatives when possible, as those have tended to help them. Mostly, though, these races turn on local issues like taxes, the local economic conditions and whether the government has been responsive to problems in that area, corruption and other scandals, health care and housing.
Updates/Corrections on the Previous Scenario-Based Posts - Three months have passed since the first one of those. Apart from that, not so much changed, though I see a couple of things I must correct.
Trump Collapse Scenario - Still looks quite possible to me. The main thing we should look at is the "Standard Trump Trial Outcomes": Trump's team has come up with a couple of delay tactics in the big trial, USA v. Dickhead (DC Court), and those ones may work, if the Supreme Court plays along. The one about immunity is doomed to fail, while the 14th Amendment case occasioned by Colorado will also fail, but may take longer to decide, as the arguments are complex. There is also a separate case being reviewed questioning whether the obstruction charge (used against very many Jan. 6 rioters) is valid to use in this case--seems also doubtful. However, the March 4 trial date Jack Smith really wanted probably will end up back a month or two, but SCOTUS could potentially kill the whole deal.
Also, I misread the 14th Amendment clause: it doesn't say what is required to be applied to diqualify; the two-thirds Senate vote is actually what is required to remove the disqualification. So what is required is very much under discussion, but I still see it only viable after conviction, though I would point out the language relates to serving in the office, not running for it! So, it could be applied after the election, before the inauguration, if SCOTUS had the courage. That would make Bush v. Gore a small-time decision.
Biden Weakened - I would say the new charges against Hunter Biden hurt him but not his electoral chances. The threat of impeachment doesn't do either; it does support the "do-nothing" argument against the House which Democrats will want to use, whether impeachment actually happens (still no effect; it would be laughed at in the Senate) or doesn't.
The Crisis Scenario - In foreign affairs, a hell of a lot has happened in the last three months, between October 7 and Israel's response, trouble funding Ukraine's war with Russia, the border crisis driven by large crowds of migrants from all over, turmoil in control of the House and the new outrageous Christian nationalist Speaker holding the office second in succession, and so on. I really don't see any of them having a significant effect on the Presidential or state races, except possibly some weakening for Democrats in Michigan. In foreign policy, it would take an actual US war involvement, not a proxy one, and the Israel-Hamas War better be over well before November, or we won't be so friendly with Israel anymore. Immigration will always be an issue, and it seems to work against Democrats at present, but claims our border has been massively overrun are made only by liars.
The real crisis is more likely to be internal. It could still be stirred up in a serious way by extremists or foreign plants, too. One example: The 14th Amendment thing could cause major riots if Trump were successfully barred from the ballot in one or more states.
Trump Out - I foresaw the possibility of the Nikki Haley stock rising. It looks likely to flower in New Hampshire, with a close outcome, but may wither in South Carolina and almost surely will do so on Super Tuesday. So let's just hope for one of the other personal mishaps for him that I mentioned.
Biden Out and Both Out (B&T) Out - Nothing has changed. Biden made a comment which showed that the main reason he's in it is to stop Trump, so if for some reason Trump definitively leaves the race, Biden might do so, if it's feasible, and maybe if it's not.
Status Quo Election--Part I, the Presidential Race - I don't see much of anything having changed, though that post is considerably more recent. Polling continues to vibrate in a fairly narrow range nationwide, and there is little evidence either the public or the Biden campaign has engaged. Subgroup tracking doesn't convince me of much of anything right now. There is a lot of work to do, huge amounts of money will be spent to do it, and it will move few voters. But maybe not so many need to be moved. In this scenario Trump will provide rich and frequent evidence of his perfect lack of qualification, in a variety of venues, and most of it will not stick to him long.
One correction: New Hampshire does not have a Senate race in '24. It will be close, regardless, but that might help the Republicans' chances to win that state slightly, as there will not be a Democratic Senator running for re-election down-ticket. Again, though, that will only matter in an extremely close Electoral College outcome, essentially meaning a 50-50 split of the six larger swing states (PA, GA, AZ, NC, MI, and WI).