What would move his base to support impeachment proceedings? After listening to some Trump supporters yesterday, I would say they would follow him all the way to hell.
Trump's base has a seething resentment of the United States government for foisting Affirmative Action on them, for foisting gay marriage on them, for insuring that poor minorities have enough food to eat - and making Trump's supporters pay for it, for putting other religions on par, or above, their own beloved Christianity.
...but they'll never be honest enough to admit it. If you read their comments on public forums - it's all there if you put it all tougher.
Trump's base also recongizes that Russia - at least the Northern western part, is all white - a fact that doesn't escape them.
