There has been a lot written on this in the last week. The consensus is that Trump has received a historically tiny increase in approval rating when compared to other presidents in moments of crisis, and that this bump has all but disappeared already. Trump's post inauguration "bump" was similarly brief and mild.
Comparing this to 9/11, which in the end will most likely taken far less American lives, it really is a tiny increase. George Bush's approval rating went up about 30%. Trump's moved a single digit amount.
