I will make a prediction of my own: If the toll exceeds, say, 100,000, we will see something akin to civil war in this country. If the southern border and lax immigration enforcement are involved in any way, the institutions and interests that advocated those lax policies will literally go up in flames.
Depending on how much power the authorities have left, and their willingness to use it, anyone who opposed measures that could have prevented the disaster could well end up in the rough and ready court of vigilante justice. This includes, but is not limited to, the PC media culture, the "peace" movement, and left-wing academia. There should have been some hangings after these forces wilfully instigated the Cambodian genocide and the green gulag in the 1970s. They can't get away with it twice, especially not if it happens here.
If you are going to win, you have to bring the fight to them where they are.
It would not suprise me that if there is another attack, we will see an angry backlash so huge that there will be nothing, nothing at all which will mean a violent one at that can be stopped.