Most attacks in the US will be preventable via the same tactics used in every day LE operations, those that aren't, will be like most LE operations, reactionary (or after the fact). Setting up security, assisting in rescue and recovery, etc.
Allowing LE to become just another branch of the military will not prevent terror attacks CONUS. Neither will trying to force the military to act as civilian cops.
Attacks here will have to be quick and sporadic. There won't be planned ambushes waiting at the local 7-11 for Officer Snuffy and his friends when they hop in mid-shift to grab a cup of Joe.
If anything, the burden of Homeland Defense lies on the shoulders of the intelligence and investigative areas of LE. Yes, we need to be able to act on intel, but not to any level that would require cops to be armed with MK19s and uparmored HMMWVs. Even if we went that route, it wouldn't stop bombers.
We don't have to become a military state to protect ourselves.
Ut ceteri vivant.