All Bush has to do is wait until some reporter asks him about this in a very public, live venue and say "You want me to fire a man who didn't break the law just because he confirmed something that everybody knew?" Put that simply, the American people will turn on the democrats so fast it'll make everyone's head spin. Persecuting someone for something they didn't do (firing them) will resonate with every single person who holds a job.
He didn't even confirm it. Rove heard it from another journalist. His response that he heard it too is just like saying, oh yeah, I heard that rumor also. That's not any kind of confirmation of anything, except that a rumor is going around.
His choice of words did not confirm. He merely said he "heard that too". He confirmed only hearing a rumor.