The principal cause of the TEA Party movement's downfall is that it gloried in its decentralization, and (from what I could tell) positively refused to organize on anything larger than a small-region basis. Which works fine on the scale of a Congressional district; but it didn't work well at the state level (how many TEA Party Senate candidates actually won?); and there was never a national organization -- and thus no coherent and consistent set of ideas, and no "face of the TEA Party" that could define what the TEA Party movement actually stood for.
And thus the TEA Party has been unsuccessful competing with the big boys on the national stage ... which pissed off a lot of TEA Party people even more than they already were. It has to be said: these some of the same angry people who brought us Trump.
The TEA party is a grassroots thing. It sure looked to me that every time someone wanted to talk about a 'national' TEA party group, it went top down, then just down in a hurry.
It is a lot like herding cats, in that the true TEA party was folks gathered around an idea, and not a Party in the capitalized sense.
As Parties go, I like the Constitution Party, simply because it is getting back to the basics.
A lot of familiar sacred cows and beloved oxen get gored in that, but they were never Constitutionally authorized anyway.
I think a lot of TEA party people looking for a political home could find one there, and that with a little work, the party could compete with the big boys. A lot of desperation (keeping the Democrat out) is involved in the current GOP support, because the Party has NOT done what it says it stands for, with a few exceptions, and those individuals who do, end up in conflict with the bulk of the GOP.
I'm not sure the GOP can be salvaged, and I think a lot of the TEA party groups broke up as the GOP attempted to co-opt them to increase the GOP base with absolutely no intention of even making concessions to those voters. The Constitution Party is already in alignment with much of the fiscal policy sought by TEA party voters because there is a Constitutional basis for sound fiscal policy and smaller government.