The market has basically been crashing since the FBI revealed it's investigating Trump. It fell sharply again on Friday, when it was clear that Trumpcare was toast. But does this have anything to do with the market losing faith in Trump's promises to deregulate the banking industry, institute deep tax cuts for the rich, and make America more business-friendly? No. That is not why the markets are now in turmoil. The problem is this: the productive economy only goes so far, can only offer so much before it is exhausted. So the gains to be made from the removal of the real costs of production and profits (pollution and so on) are limited. The real money in our world today are yields from very risky investments. Nothing else makes that quick of a buck.
But only a few people can take such risks fearlessly. For most investors, there is real fear about losses. But if there is certainty that the government will cover losses for big risks, then all investors will make them. This is called moral hazard ("when one person takes more risks because someone else bears the cost of those risks"). And Trump, who unexpectedly beat Hillary Clinton, looked like he might be invincible, like he had something special, special going on. Markets are not rational but psychological—this is the wisdom of Keynes, the greatest mainstream economist of the 20th century.
An invincible Trump, in Wall Street's eyes, would always make sure that the state recovered the losses of risky investments. But a Trump who can be checked or who is not magically (even satanically) all-powerful means risky investments are simply that: risky investments. Expect investors to pull money out of the market because they fear losing it doing real business, doing real capitalism. They want socialism to back their speculations.