Three potential explanations for that abortion of a tweet:
1. Trump's hard-on for authoritarian regimes has extended to the domain of the "Little Rocket Man." Russia is pretty friendly with the DPRK, so maybe Putin has told Trump that he should make nice, not war. 2. He's trying, in an incredibly cack-handed manner, to justify ruling out further efforts of diplomacy with North Korea. 3. He's calling Kim Jong-un fat.