“US military should have a high-level task force to fully investigate these incidents and target the attackers involved for severe reprisal.”
A nice idea, but we can’t even keep our troops anywhere near Iraqi population centers without high losses; they’ve pulled them back to remote bases, and they’ll operate as mobile strike forces from there, but these attackers (and a large number of other Iraqis) are part of the general population.
We can't guard the churches. That might backfire anyway. However, we should make it a priority to find out who is behind the attack. Which imam, tribal sheik, cell group, or militia did this? They should be hit them extra hard. That might give the Christians some breathing space to survive, even as our presence scales back. Otherwise, our legacy may be said to include the ethnic cleansing of Christians from Iraq.