Trump obviously hates Obama for reasons best known to him. Throughout the Obama presidency, Trump attacked Obama, both in person and his policies. It even got worse after he became president. Hardly a day goes by without Trump mentioning Obama. Some say it's due to jealousy, as Obama is as popular in the US as Trump himself. In the survey that came out last week they were tied on popularity.
Outside the US, it a no contest, outside maybe Saudi Arabia and Israel, Obama is almost worship in foreign countries, while Trump is hated. The straw that broke the camels back was when Mitchell Obama was voted the most admired woman in the world, when his wife Melania did not even register on the scale.

So you can understand how furious Trump must have been as he spent most of his speech on the Iran's missile attacked on US based criticizing Obama. He blame Obama for everything except launching the missiles itself.

I want to show a video where Obama took on Trump while he was still president. He threw jibes at Trump's in a cool calculated and intelligent manner. Obama is a master orator.

https://www.youtube.com/watch?v=7eJpWOY3r18

We must remember the Obama Roast when dealing with those with orange noses. He completely outclassed him.