Rubio was simply saying that a positive development to result from the attacks was that it might make the U.S. take the threat of terrorism more seriously. I disagree with Rubio, and think the U.S. has already traded too much security for liberty in the War on Terror, but let's keep this in context. He never said the attacks were good for his campaign.
It's a damning soundbite, and it will be used in a "in case of emergency break glass" situation.
Eh, I'm sure TRUMP will make good use of it very soon.