The greater principle at stake, related to oversight, is the principle of the rule of law. As with legislative oversight, the rule of law is already dead. The extent of the crimes that the President has committed is staggering. He admitted, on national tv, to the very thing that forced Nixon from office-- firing the FBI Director to shut down an investigation into corruption within his campaign, for starters. And as I have said, repeatedly, Trump will 100% get away with everything. The probability of impeachment is an absolute 0%. The probability of him ever facing any criminal charges for anything is an absolute 0%. I'm not even going to use "epsilon," which is the Greek symbol we use for numbers arbitrarily close to but not precisely equal to zero, as a statistician/weasel number. These probabilities are precisely zero. They are absolutely, mathematically impossible outcomes, in that they violate basic laws of physics, and fuck quantum mechanics.
So, what does any of this have to do with 2018? Short version: the rule of law is dead. The question is the extent to which this fact is shoved in our faces. Following from yesterday's basic point, a GOP majority in both chambers of Congress means that Congress can continue running interference for Trump and blocking any legislative investigations. Keep in mind what Devin Nunes has been doing. He hasn't just refused to investigate Trump. He has launched counter-investigations into the FBI, Mueller, spread insane lies, put out that loopy "Nunes memo," and all the while, ran directly into Trump's lap to tell him any time anything was coming down the pike. That's what happens as long as both chambers stay GOP. Most of that, though, is invisible to anyone who isn't a hardcore politics junkie. That's the point. What most of the country hears as a result of Nunes and his bullshit is just noise. That's the point. All the GOP has to do to protect Trump is to scream nonsense loudly enough to crowd out the facts. That fact that it's nonsense doesn't matter. The volume is what matters. This is why lies, and liars are so dangerous.
If Democrats get the House, what happens? Republicans can still pull stupid stunts, and they still have Fox News and the rest of their media operation, but they lose the ability to launch counter-investigations from the House. In principle, Richard Burr could start, but he isn't as much of a Trump-tool as Nunes, and he has actual work to do. The House, meanwhile, has investigatory powers beyond trying futilely to subpoena people who will simply claim executive privilege, and the FBI under Trump has gotten leakier than a Russian hooker in a hotel room with Trump.
You're never going to see Mueller's report. After the election, Sessions probably gets fired, along with Rosenstein. Mueller gets replaced, or put on a very tight leash, and when he does finish his report, it gets buried. The probability that Trump faces any legal consequences for his actions has always been a precise, mathematical zero. However, if the Democrats get at least a majority in the House, they can force some information to the surface, and prevent the GOP from using the House Select Intelligence Committee from running a counter-operation on Trump's behalf, the way Nunes has been doing.
What is the consequence of that? For the rule of law, nothing. The rule of law is as dead as Cleese's parrot, either way. However, control of the House has an impact on the extent to which that is obfuscated, and the extent to which information is laid bare to the public about the criminality of the Trump Administration and the campaign that led to it. Trump himself will never face any legal consequences. He is the idiotic, spoiled little shit villain of every '80s movie, and he gets away with it because of his daddy, just like always. What that means, and how we deal with unpunished criminality run rampant depends on the extent to which the public is forced to face it, and the 2018 election has some impact on that.
If it sounds like I'm saying we're already fucked, and the question is merely the difficult, un-fucking process, that's about right. And I'm not done. Still, we are in abstract territory because in concrete terms, we're wearin' concrete shoes. That's what happens when you make a mob boss President.
I'd rather have Uncle Enzo, personally.