I don't believe Congressional Rs care one bit about tRump's cratering poll numbers
Their own numbers have been scraping bottom for years and years. That hasn't stopped them from lying to the electorate, nor has it given them pause to change their policies away from their full frontal assault on everyone who isn't at least a millionaire. They simply don't give a fuck.
tRump's numbers incredibly low? So what? They control the government at every level. EVERY level. Soon, they'll have a majority on the SCOTUS, which has been an actively pro-R institution for years. They know their policies are wildly unpopular with the American people. They simply don't care. They've figured in the pushback they'll get from letters and phone calls - they can ignore them while their staffs deal with it. Townhalls? Big deal. You face your constituents for 90 minutes every two years or so. So what if they're screaming at you? You'll be back inside the D.C. bubble before most of them make it home from the townhall.
Pressure is good, yes. But let's not kid ourselves. The AHCA failed because it wasn't evil enough from the Tea Party perspective. All those "moderate" Rs were lined up and ready to pass the thing WITH the elimination of basic services that was put in to entice tea partiers.
And look at all the other anti-American things they're doing that are garnering Congressional suppprt. Things like blocking the Russia investigation, etc.
The Rs have made the calculation, and they are fine with taking a little bit of heat as long as they can push through their destructive agenda. We are a long way off from them turning on tRump.