Consider what the left did after 9/11. The left just went into hiding. The MAINSTREAM reared its head like the sleeping giant and the Taliban fell.
What would Americans do? They will do what they ALWAYS do. The same after the Alamo, pearl harbor, 9/11, or any attack that enemies think will be a setback.
The leftists (and they are really just the democrat party) is really a enemy of the usa. They are not "loyal opposition" they are just opposition.
I'm sure it would bring out the hatred & patriotism. Initial reaction by people on site would be surprising. The people that you would think would keep it together; completely lose it and cry like babies. The ones that you wouldn't think of as leaders are the ones that take control and help the survivors out. No joke.