It was one thing when Donnie was an asshole who couldn't get anything done. The tax bill and repeal of net neutrality changed all that. Sure, they're both "accomplishments" most people hated but, as the old song goes, "nothing succeeds like success," and even taking on the semblance of effectiveness is going to boost his image significantly. As he surely knows, "everybody loves a winner"...or, if they don't exactly love him, they at least don't have contempt for him anymore.
But the biggest thing giving him the momentum is the absolute hash we made of last weekend's shutdown. It gave Trump and the G.O.P. a major victory (even anti-Trump journalists were writing about him and his party "dancing in the endzone" after we backed down). Now, in order to save DACA, we're going to have to go hat-in-hand to the White House and accept any terms he lays down (including his border wall and a 50% cut in legal immigration) or else see the Dreamers deported. The first option will give him massive credit, the second will earn us massive blame. Heads, he wins; tails, we lose.
So, yes, I see DJT on the upswing right now. Of course, he might find a way to screw things up again (but tweets and other examples of outrageous personal behavior won't do it...his antics have become normalized), but, as it is now, I'd expect his popularity to climb over the next few weeks/months; not enough to actually make him popular, but enough to narrow the gap so that he won't be a irreversible drag on his party in the midterms. And, from then on...? But he couldn't have done it without our help...