I absolutely agree that things in the US seem to be going in a bad direction, but we haven't yet lost our constitution or system of checks and balances.

There's a big difference between the Constitution, law, and doctrine. The Monroe Doctrine, for example, was little more than policy and had nothing to do with law or constitutional rights.

Our checks and balances are still there, the problem we have today is the lack of willingness for those with the power to actually use them. Congress can stop Trump on many of the things he's doing, for example, they just don't want to and have instead continued a decades long pattern of Congress ceding power to executive. The judicial branch has at least stepped in at times, they really don't have to as the Supreme Court can choose to simply not hear a case.

The issue of lying politicians is as old as governments. If we want to focus on Trump as the issue here, and he's a big one, you only have to go back to the pandemic to find politicians on the other side of the aisle blatantly lying to the public without consequence.