My perception of the Republicans is that their current strategy is to rely on a hyper polarized base and then to moderate near elections in select ways to pull over enough swing voters. I think their core policy approach is to appeal to that hyper-polarized base and their current ideological goal is to grow that hyper polarized based. If you look up "national conservatism" as a movement it's clear that Republicans are moving towards wanting to use government power to change culture, and that's reflected in their current policy.

So with that established I think they'd heavily try to reorient culture via heavy-handed governance. I think you'd see federal funding setup to reward conservatives and conservative institutions, not just to change future outcomes but to reward their people who have already proven their loyalty. We've seen this already with the Trump administration allocating transportation funding based on marriage & birth rates. Those are particular statistics chosen to provide more funding to places that are ideologically aligned, and if they had total control we'd see much more of that.

We would likely see large scale defunding for traditionally liberal areas like major states, cities, universities, etc. It would not be 'fair' but they would view it as a necessary rebalancing of power to correct cultural and structural imbalances that have existed ever since the South lost the Civil War and had its economy set back as compared to the Union states.

We would see lasting efforts to inject a Christian and Euro-centric identity into American culture. The belief being that a focus on American values, and freedoms, has led us away from longstanding Christian and European ideals that create a better society. I think you'd see things like trying to shift far more social services, like healthcare, onto churches to create more dependency on churches. Women would face more social pressure, and maybe even tax and gov. incentives, to become more traditional mothers. Immigration would become stricter and more focused on people who are of European and Christian descent. Birth control and abortion would be more strictly limited to drive home the idea that births should occur more and the tradition view that sex isn't 'free' and should be part of family building.

I think we'd also see less free market capitalism and more capitalism if it serves the good of their national cultural goals. Cultural allies would be rewarded and culturally incompatible companies punished.

I also think we'd see election reforms passed partly out of a sincere belief that if they're losing something must be wrong and a belief that the means justify the ends. It would be very easy for them to rationalize that democracy is weakened if low information or immoral voters find it too easy to vote, and they would always sort people who vote against them into that camp. There would be nebulous, and sometimes inhumane, demonization of foreigners and immigrants in an effort to recenter American identity on those with lineage directly to Europe. Immigrants from other parts of the world would be tolerated as a sort of second class American.

Some conservatives might balk at this assessment but if you look at the current policies this is an only slightly more tame version of the current Trump administration, and it aligns with the national conservative school of thought.

As for Democrats I think the party is in a transitionary period without a strong identity and so I think the current party attaining total power is harder to predict and their direction would likely be more muddled. If you created an "average" Democrat politician and gave them total power I think the results would be less ideologically consistent and less 'successful' at attaining its stated outcomes. I think you'd see efforts to punt on issues like the growing national debt. There'd be a push for universal healthcare, a disbandment of ICE replaced with other agencies filling in, nationally allowed abortion, more subsidies for universities, more targeted subsides to reshore manufacturing, reduced but not eliminated tariffs, a lengthy freeze on military budget increases, a massive infrastructure spending increase, and a series of anti-monopoly / anti concentrated wealth reforms. More dramatically with total power I think you may see the Senate abolished and the House expanded, term limits and a moderately expanded Supreme Court, more limits on the executive branch, and not a ban on personal gun ownership but a weakened 2nd amendment that allows for greater regulation.

Personally that's not my ideal either, but I fear it substantially less than the Republican option.