Personally I think they are both being asses, Obama for Trolling, and Trump for getting hooked. Trump is VERY easy to figure out - he's thin-skinned, reactionary and easily trolled ( something that is seriously concerning for the man who will be in the Oval Office - but that's another story). In other words it does not take a lot to get him going and ounce going, he typically puts his foot in his mouth.
You could tell that, this was a strategy that the Dems and Clinton used in The Debates - say something that would get Trump going, step back and then let him go! Then he's rambling on incoherently, often way of script/topic and even arguing/debating with the moderator! It was risky for Clinton to do this - and I think it failed somewhat. From a truly standard way of scoring a debate and using a base of who would be the best president, grasp of issues etc . . - Clinton "won" the debates. But Many watchers, who don't really know what a debate is about, care for classic debate protocol/process or who had deeper knowledge of the issues (and that was MANY viewers), probably thought Trump "won" The Debates - because he simply, talked the most!
Steve Fleck @stevefleck | Blog