Its kind of hilarious that they actually think they can do all this stuff when they so far have utterly failed to do anything major. Welp we completely failed to accomplish anything with healthcare lets move on to something just as complex and divisive with absolutely no plan for what we want to do.
That's actually why some think they can pull it off, because the GOP is increasingly desperate to pass something that they can point to as an achievement. Before long, they'll be introducing something like "S.173 The Pumpkin Spice Latte Act" (making pumpkin spice lattes the official drink of autumn) just so they can pass something.
Problem is, as they get increasingly desperate, unscrupulous folks introduce more and more bad shit into bills in the hopes of "Well, normally this wouldn't stand a chance in hell of passing, but maybe now..." which then causes the handful of Republicans who still have a spine (and/or brain cancer) to shoot it down. It's a vicious cycle.
And as noted, it doesn't help when you have Trump basically going, "Pass something, you morons! Why the fuck won't you pass my bills, you shitheads? What have you got against me, you low-energy losers? Why do you hate America? I'm going to back your opponent next year!"
How to Make Friends And Influence People: Trump Edition
EDIT: And on the tax reform in particular, he's lost a ton of credibility on fiscal discipline by adding to the budget deficit after campaigning as a deficit hawk. That's where he's losing the Rand Pauls of the world. Meanwhile, you have Mick Mulvaney, the OMB director and largely the author of Trump's budget arguing that
they've given up trying to cut spending because it's Congress's fault. He tried to make the classic trickle-down growth argument, which is that "Ok, since we can't cut spending, we'll lower taxes and that'll spur tons of growth, which will increase revenue."
John Dickerson rightly called him out on his bullshit.
Republicans for a long time have talked about spending restraint. And so to now say, "Well, we're going to do it through growth," that's a big- that's no small deal. It's like Weight Watchers saying, "Well, we're going to give up the dieting part."