There is no lack of commentary on the prospects under a Trump presidency, but in my view one thing has been missing. It is that Democratic control of Congress would be insignificant. A President Trump would not be bound by ordinary Congressional constraints. He would marginalize an uncooperative Congress, just as Republican state legislatures under shield of gerrymander and voter disenfranchisement move to disempower victorious Democratic candidates for governor.
We have already seen this during his first term in office. There used to be something in the Constitution called the Emoluments Clause. This made illegal the practice of a president personally, financially profiting from his office. Trump violated this openly and repeatedly. Congress could do nothing. An impeachment count in this vein would have failed like all the others, for lack of a required super-majority in the Senate. Such a super-majority is precluded by current, pervasive voter suppression regimes throughout the nation that lock in Republican-majority state legislatures, without regard for actual voter sentiment.
In the 19th Century there was a case when the Supreme Court ruled against the preferences of President Andrew Jackson, one of the worst people to ever occupy the White House. Jackson responded, ““The decision of the Supreme Court has fell still born, and they find that it cannot coerce Georgia to yield to its mandate.” This is commonly remembered, inaccurately according to the source linked above, as “John Marshall (Chief Justice—mbs) has made his decision; now let him enforce it.” The upshot is that the president has legions of employees who do what he says, and the Supreme Court does not. Of course, now Trump has bought himself (with other peoples’ money, as usual) his own Supreme Court.
We have all heard of plans being formulated at the Heritage Foundation to purge the Federal civil service and replace them with political cronies who can be removed at will. How would a Democratic Congress prevent Trump from doing whatever he likes? The national government would be reduced to two branches, the Executive, under the thumb of Trump, and his own Supreme Court majority. In the face of monopolized executive power, the law counts for little.
I sometimes think the great allegorical cartoon of our times is the "Far Side" single-panel where a circus bear, with his muzzle in his hand, says to his fellow bears "Hey, what do you know; these things just snap right off!" The bear of course is the contemporary GOP, and the muzzle represents all those restraints enforced by Custom about what office-holders can't do, because... it isn't done! And the trainer in the background, putting another circus bear through his routine, is the remnant of Democracy which is about to be torn to pieces.
I would say that Congress still has the power of the purse. But that doesn't mean much, I suppose, if every morning Trump would pardon the latest violators of the Anti-Deficiency Act. And I don't suppose that Trump would care much about the subsequent opinions of Mr. Market.