I'd definitely address gerrymandering if I were writing this today. I don't have a good answer for why I didn't back then.
Of course, the crazies have grown in number and in lunacy and have grown more dangerous. Now a plurality and possibly a plurality of one of the two major parties holds demonstrable delusions among their core political beliefs.
If the crazies leave, the Republicans cease to have a viable party.
The GOP needs the crazies more than the crazies need the GOP.
Now let's generalize the idea somewhat. Let's say you have N shareholders whom you have brought together to form a majority. Some of the members of your alliance have a large number of shares, some have very few, but even the one with the smallest stake has enough that if he or she drops out, you will be below 50%. In this scenario, every member of the alliance has equal veto power.
I apologize for the really, really basic fun-with-math explanation, but this principle has become increasingly fundamental in 21st-century politics. At the risk of oversimplifying, elections come down to my number of supporters times my turnout percentage versus your number supporters times your turnout percentage. Arguably the fundamental piece of the conservative movement has been to focus on ways to maximize Republican turnout while suppressing democratic turnout. (Yes, I'm leaving a lot out but bear with me.)
There are at least a couple of obvious inherent dangers in this approach. The first is that there is an upper bound for turnout percentage. This is especially worrisome when the number of your supporters is decreasing. Sen. Lindsey Graham was alluding to this when he observed that they weren't making enough new old white men to keep the GOP strategy going.
There is, however, another danger which can potentially be even worse. When you need nearly 100% of your supporters to show up to the polls in order to win, you create a situation where virtually every faction of your base has veto power. One somewhat perverse advantage of the large base/low turnout model is that groups of supporters can be interchangeable. You have lots of situations where you can alienate a small segment but more than make up for it elsewhere. In and of itself, this allows for a great deal of flexibility, but the really important part is the power dynamic. You have to represent a large constituency in order to wield veto power.
Probably since 2008 and certainly since 2012, pretty much every nontrivial faction of the GOP has held veto power which means the question is no longer who has it, but who is willing to use it. The Tea Party was the first to realize this. Now the alt-right has caught on to the dynamic as well.
Even with increasingly aggressive and shameless voter suppression techniques, Republicans tend to get fewer votes. It is true that they have, through smart strategy and tactics, managed to get an extraordinary number of offices out of those votes, but it is a precarious situation. We can debate how many people really believe in shadowy Jewish banker conspiracies or Martian slave labor camps, but it is almost certainly a large enough group to sway some close elections if the crazies collectively decided to go home or, worse yet, opt for a third party.
Ed Kilgore (whom I follow and generally respect) had a badly ill-informed post, Trump Should Emulate Buckley and Tell Racists: ‘I Don’t Want Your Vote.’ That simply won't work for Trump or the GOP. They need the crazies more than the crazies need them.