A comparison between opinion polls taken ahead of a potential airstrike on Syria for alleged chemical weapons use in 2013 with those taken in the aftermath of the recent airstrike on the same country with the same leader for the same purported reasons, shows the power of cognitive dissonance to make people rationalize outcomes that they preferred not to happen.
Rewind to 2013, back when Trump was firing off tweets against the airstrikes on a daily basis. Every poll showed overwhelming opposition to such strikes, even when the question was worded to state as a matter of fact that Assad had used chemical weapons on his own citizens (ABC / WP), and even when a separate question found 80% agreeing that Assad had used chemicals on his own people (CNN).
Majorities agreed with anti-globalist positions across a range of questions (Pew / USA Today), such as airstrikes will make things worse in the Middle East, we have no moral obligation to stop violence against civilians in another country, Syria poses no risk to us anyway, and we're not going to lose credibility just because we don't fire missiles.
Republicans were more opposed than were Democrats, compared to the opposite now -- kneejerk partisan reactions. But Trump campaigned during the primaries and general that we should not do what we just did, and he blew away his anti-Assad rivals. So it's not like Republicans had changed their position as of a few months ago.
The main difference between this strike and the potential strike in 2013 is that Obama tried to argue for it in the court of public opinion, and that campaign dragged on and on as he refrained from pulling the trigger. That allowed Americans' true feelings to crystallize, and it turned out they were against it. This time, the Deep State pulled the trigger as soon as they could, after some pro forma propaganda about the evil butcher gassing beautiful babies. That rapid-fire response gave Americans little time to evaluate the situation and let their anti-airstrike views crystallize again.
After the strikes had already been conducted, a good chunk of people who were against them will not want to feel like they were on the losing side of that decision, so they rationalize after the fact that they actually approve of them when a pollster calls them up. There's no point in crying over spilled milk.
We can tell that people didn't actually want these strikes because the typical "approve" response is that they were fine, but let's not do it again, and definitely do not send in a ground invasion. They're just trying to rationalize this specific act, and move on.
If they were so against Assad or his regime or his Russian patron, they would be tasting blood by now and be excited about future strikes against the evil dictator. That's how the neocons have reacted. But only a small minority of American citizens feel this way, probably the same people who were looking forward to strikes in 2013.