I fly weekly, through multiple domestic airports. I have seen absolutely no evidence that there's any additional effort, using dogs or armed police officers, to prevent a Brussels-style attack. IOW, I don't see what you're suggesting is taking place.

What I have seen is a massive scrutiny of carry-on bags at the x-Ray machines and post-x-Ray, with subsequent delays.

As is typical for TSA, they focus on prevention of past threats or correction of criticism, not on current threats.