On the downtime side, I doubt any otl politician will be getting their vote. The MAGA crowd I think is more likely to pick from their own numbers, there's too much of a divide between 2020 culture and 1970 culture, downtimers won't have the right slang, know the right cultural references, or even have the right speech patterns to sound authentic.
Ironically if they do, they'll probably vote Democrat. Donald Trump was a card-carrying Democrat at this point, before the party moved so far left he was left on the right. The Republicans meanwhile have moved far further left than they were then, even the more progressive people in 1970 wouldn't be as gung-ho for things like gay marriage as current conservatives are.
On the technology front the US is now 50 years ahead and has foreknowledge of several key events. This advantage won't last, there're scads of foreign students who are more loyal to their homelands and historical knowledge can be plucked casually from every library, even closing them all there's zero chance the KGB can't get somebody to sell their high school history book for five grand. Some massacres and events are butterflied away, others are going to be caused, unfortunately. The US has lost a lot of natural resources that hadn't been mined yet but the advancements available in resource extraction will make up for it. The US currently doesn't have a great manufacturing base but I suspect the part that didn't stay downstream is going to be rebuilt, and stay in the US this time. Technologically, the US is going to be hyperdominant for some time.
Knowing that it's going to be a contentious issue for at least the next 50 years (and probably painted as the next Dredd Scott by the uptimers), I suspect Roe vs. Wade won't come up at all in 1973 and if it does, will be judged differently with at least a significantly different line of reasoning behind it.
The US in 1970 has a bit over half the total population the US had in 2020. However, it had a much higher percentage who are rural than the modern day, who they'll lose. The MAGA group is going to outnumber the downtimers significantly and will be a deciding bloc until they split up and start arguing among themselves.
Israel will discover that the Palestinian situation will never be resolved, will never stop getting their people killed, and may well decide to do something drastic to rip off the bandaid given how things turned out.
The USSR's reaction is going to be interesting. They know now that their nation is going to fold like wet tissue paper, and that further, the US's tech advantage is so high they can roll up the USSR's entire military if they make any serious effort. The USSR is truly between a rock and a hard place and they could well decide to do something stupid with their nukes before the US can crush them utterly.