In terms of policy, what is at stake? In direct terms, taxes. If the GOP keeps both chambers of Congress, they pass more tax cuts, because that's their thing. Tax cuts. That has short-to-medium term consequences. The last round were passed under "budget reconciliation" rules, which meant that the corporate tax cuts were "permanent," but some other parts weren't in order to keep the bill theoretically deficit neutral over 10 years, and there were tax increases in the bill, but they will pass tax cuts on their favored constituencies. The result? Depends on who gets the cut, what else they do, the time horizon, etc. Note my sarcasm-quotes for the word, "permanent," though. No change to statutory law is actually permanent. All it takes to change the tax code is another bill passing. Why don't tax cuts get undone? Essentially, because the Republican Party has won the public argument. In 1984, Walter Mondale ran against Ronald Reagan saying that regardless of who won, taxes would go up. Mondale said that he was being honest about it, and Reagan wasn't. Mondale lost the election, ostensibly for promising to raise taxes. In fact, a lot of people's taxes did go up in the 1986 tax reform bill, which Reagan signed, but oh, fuck history, right? Democrats started getting really scared about promising to raise taxes after Mondale's landslide loss in 1984. So, tax cuts don't tend to get undone. Those victories are sticky. Some of Bush's 2001 cuts were allowed to expire, and there were some tax increases snuck in under Obamacare, but Democrats are pretty twitchy about raising taxes. So, if the GOP keeps both houses of Congress, they cut more taxes. That has an effect. For a while.
Beyond that, it is hard to see direct policy stakes. I'll get to other implications, but what would the GOP do, actively with a majority? Make another attempt at Obamacare? Maybe, but remember that their margins in the House get slimmer. If they manage to keep the House, which is possible, it will be with a razor-slim margin, and it was hard enough as it was last time around for Ryan to get anything through. They could easily fail in the House. The Senate? They could easily pick up a seat (bye, Heidi!), bringing them back to 52, but that's where they stood last time they tried, and things didn't work out. "Skinny repeal" failed when Collins, Murkowski and McCain voted no, but then passed when they included it in their tax bill, but they couldn't agree on anything else. If they make another attempt at a "replace," they've got the same problems, except that the House is harder, and the rhetorically appealing part of their war on Obamacare-- the individual mandate-- is already gone, so they can't use that as a sweetener. What's left? It could be harder, not easier, and last time was a slog.
What's left, policy-wise?
More tax cuts!
And if the Democrats get at least one chamber? Gridlock. That's it. Gridlock. So, tax cuts versus gridlock. In policy terms, those are the stakes. Now, there is plenty more to discuss, when addressing the courts, appointments, subpoenas, and all of the other fun stuff going on, but let's be clear about the policy stakes here. They aren't that high, unless you think the next GOP tax bill is the most important bill ever.
I don't.