How much lower can the democratic party go with the white vote?

Donald Trump's 58-37 margin among whites is the third largest in all the elections in which we have data (1972 and 1984 are the two highest, where the gop won whitey by 32 points (!!)).

He did this while doing much worse than republicans historically do with upper class whites and educated whites, who were turned off by his lack of political experience and his economically tyrannical talk on trade.

IF trump appears over the next 4 years to get things done that those upper middle class whites approve of such as lower tax rates, less regulations, healthcare reform, etc, while also managing to walk the walk with working whites, he could soar again to those +30 margins we saw with the reagan and nixon.

I figure there will always be a floor of around 32-33% of the white vote for democrats. This includes ancestral union workers, government employees, and yuppies in places like denver that have fringe views on things such as sexual restraint, death penalty, and law and order.

My point is that it should scare democrats A LOT that trump won whites by more than romney did (+20 vs +21) given he underperformed him bigly with traditional republican groups such as rich whites. If he can show enough competency to win them back to romney levels, while maintaining ussr-like numbers with rural whites, he will win reelection, because there simply are not enough minorities in places like wisconsin, minnesota, and michigan to stem that tide.