When hiring a new employee, you cannot simply go on their words alone. You have to pry into their claims on their CV. You have to call their references.
The bottom line: the best way to predict someone's future behaviour is to look at their past behaviour.
Looking at Trump's behaviour, anyone who is heading an investigation into his ties with Russia gets fired.
Think about that for a minute: the people who are meant to be making sure Trump is doing things legally, the people who are meant to investigate and make sure that a sitting President did not commit Treason and collude with a foreign power, have been fired for doing their jobs.
I've heard the saying used often recently: Where there's smoke, there's fire. Despite repeated denials from the Trump campaign things have been smokey for a while now...but nobody believed that Trump would be foolish enough to fire Comey while he was investigating Trump.
Trump proved them all wrong.
So, we can no longer count on anyone to be able to rein in (or even investigate) Trump's potential treason, his likelihood to steal from the American public, or his unprecedented nepotism. Never has there been such a clear, obvious, and intentional attack on the United States' form of democracy.
We owe Trump a thanks, really. He's made things quite simple: Either we impeach Trump and remove him (and his family) from office with prejudice and quickly, or we give in and throw a hell of a coronation for King Trump (Comrade Trump? Supreme Chancellor? High Priest? Chairman? What's his title going to be? Does it really matter? Probably should be unisex though, as his daughter will need to wear it after he passes away.)
The United State will no longer be a Republic of States, but rather a dictatorship with trappings of democracy but without the substance.