Obama and May are proper politicians. I think they believe in what they do, even if they stretch the truth sometimes. They also do it diplomatically.
Trump has the diplomatic skills of a pit bull. His politics seems to be run off the back of a fag packet (sorry fag is British for cigarette - no offence meant).
Kennedy, before his speech about the Cuban Missile Crisis, ran it past several people, even Eisenhower, before giving it. By contrast, Trump's "fire and fury" outburst came apparently from nowhere during a press conference, and his own team, clearly surprised, had to play it down.