Interesting article on Trump compliments:

http://www.esquire.com/news-politics/a49875/donald-trump-twitter-compliment-insult/

"Donald Trump is nothing if not consistent in his inconsistency, and one of his most dependably erratic practices is abruptly turning on someone over whom he had just recently gushed."..." To find out, we plumbed Trump's Twitter history and counted the days between a compliment and spite."

eg Chris Christie  1,333 days.

AngelaMerkel  797 days

George Bush 37 days

etc