Congress and the Constitution are cited in this argument as if they are the only two checks and balances that Amercian democracy has in place. But there are many others; and one of them--the most important one--is the people themselves.
The truth is that, when all is said and done, the people are apathetic about what goes on in the government; they care more about culture and how that is affecting their lives far more than any politician ever could.
They may be jaded, believing that their vote doesn't count, that all politicians are liars, and that what the privileged elite want is what ultimately happens.
Democracy does work. But it only works when all of its parts are working together. If the American people were to stand up and take action, they would be the ultimate and final check and balance that puts the President in their place when things get out of hand. But the American people are apathetic to politics, caring only marginally about the inner workings of the government when it directly affects their lives. Trump's wall didn't affect the majority of Americans. That's why they let him get away with it. If they really didn't want him to do it, they would have stood up and fought. And the people would have won; democracy would have won.
Democracy isn't the issue. It's the people who are the issue; both those in charge for their corrupt and selfish intentions, and those being ruled for their lack of interest in the government at all.