First they have to deal with Obamacare. Nobody has ever figured out just what Obamacare is doing and what it is gonna cost. The health insurers are dropping Obamacare as fast as the can after loosing barrels of money. Right now it looks like Obamacare promises taxpayer funded health insurance for everyone who doesn't have health insurance from their employer or is 65 years old and hence eligible for Medicare. Nobody has ever published an estimate of what Obamacare is gonna cost. A reasonable guess is it will cost as much as Medicare. There are more people without employer health insurance than there are people over 65. Since they are younger than 65 they ought to be in better health. Any way you slice it, Obamacare is a black hole down which we toss money. A lot of money.
To do tax reform, we have to get a handle on Obamacare costs. Unless we at least know what the taxpayers have to fund, you cannot do any tax cutting. And every one agrees that taxes are too damn complicated, too damn high, and too unfair. If tax reform doesn't happen, there will be a LOT of unhappy campers for the 2018 by election. Might be enough for the Republicans to loose control of the house or the Senate, or both.
It's do or die time for the Republicans. They have to reform Obamacare. They have to do tax reform. If they don't, they are gonna get clobbered in 2018.