The two most conservative groups are stuck reacting to each other. The first, more Trump-skeptical group would gladly help get rid of Trump but are terrified of what might happen if their fingerprints are on the political murder weapon. The second, more pro-Trump group will stick with him for as long as possible, and many will stick with him to the end.
That leaves the third group of unideological swing voters. They want real things from Trump. They hope for social regeneration but will settle for steadier, higher-paying jobs and no more lost wars. If Trump fails to deliver on those expectations, some of these voters will walk away from politics for a time. Others might well support a Democrat who didn’t obviously hate them for even thinking about voting for Trump. If this group defects from Trump, his numbers might decline enough that the Trump-skeptical conservatives would be emboldened and some of the pro-Trump conservatives would decide that Trump is more of a loser than a fighter (though that will be a tough case to make since, after all, he did win the election).
So, who would be the bellwether that Trump’s support has collapsed? It might be an ideological conservative who has tried to expand his national profile by appealing to unideological, wage-earning populists, and whose political success is dependent on former Clinton voters.