This has just come to my mind, though I'm sure it must have been quoted before on earlier threads.
“Power tends to corrupt and absolute power corrupts absolutely. Great men are almost always bad men, even when they exercise influence and not authority; still more when you superadd the tendency of the certainty of corruption by authority.”
Though that would tend to imply that Trump is a great man, but he is only a legend in his own mind.
Did someone say that Republicans are finally seeing reasons to impeach Trump, because by leaking state secrets he has broken his Presidential oath, or is it just wishful thinking on my part?