My progressive friends will say this is because Trump is uniquely unfit for his office and to rebuke him (politely, in this case) is only what is proper in all right-thinking people.
On the other hand, can you imagine any foreign leader contradicting the Pres. of the US in public -- on US soil -- back in the day (other than the leaders of the Soviet Union and, maybe, France)? It just wasn't done. No matter how much they might fume and fuss in private at whatever President's goals, they needed American goodwill too much. Obama has so devalued American leadership that American leaders can be lectured by foreign leaders on American policy on American soil, and not feel that they risk anything to do so.
I wish Trump would be more measured in his pronouncements and run a less chaotic office. I'm probably going to be disappointed in that hope. Still, he isn't necessarily the biggest wackadoodle we've ever elected. Woodrow Wilson was an egotistical (and racist) crank of the first order, but as the leader of the only undamaged economy at the end of WW 1 he had the leaders of Europe fawning all over him.