I don't have a very complicated view of this on a surface level. This is it:
The "normalization" of Trump that I most fear is the Democratic leadership's support for this action. You cannot separate the action from the man in this case; it's the man who is dangerous to the world. He needs to be opposed at every step.
As for Syria generally, I don't think there is a solution. Without one, we need to be circumspect in what we do. For some reason, Assad did not use his chemical weapons with Obama in office after the original transgression. Something changed since. I'm not expert, so I'm not sure what. But there was a tenuous balance the Obama administration seemed to reach among the US, Assad and Putin, and no more sarin.
Obama asked Congress to approve action against Syria, and Congress rebuffed him. There is a popular belief among the Right that Obama was "weak" and that this was a cynical move to avoid having to do anything about Assad. I thought that even if he were being completely cynical, asking for broad support before engaging in another Middle East war was appropriate. It's not just that we learn nothing from history, it's that we learn nothing from what is still going on.
When you see that even Trump can gain support from a lot of Democrats and Obama could gain none from Republicans (who have totally reversed their principles for some unknown reason), it shows the asymmetry of the parties.
That's the last point David Frum made here. Although Frum is more of a Hillary-type Republican in that he believes in intervention abroad to assert US influence beyond its interests, he has a lot of interesting qualms here.
But it's this that gets me (emphasis mine):
Trump Is Lucky in His Opponents
“The secret of our success in government is that we did not have us in opposition.” That quip from a friend in an allied government applies with even greater force to the Republican Party of the United States. Trump’s action has gained support from Democrats that was never available to Obama from Republicans. In the fall of 2013, even the hawkish Marco Rubio—who had long called for action in Syria against Assad—nevertheless opposed Obama’s request for authorization to do just that. Rubio’s explanation focused on the flaws in Obama strategy and commitment. “I remain unconvinced that the use of force proposed here will work … I believe that U.S. military action of the type contemplated here will prove counterproductive.”
Rubio’s points surely had some validity. Surely they apply even more forcefully today—yet Democrats from Chuck Schumer to Nancy Pelosi to even Elizabeth Warren have offered support for Trump’s actions. Pelosi praised the action as "proportional.” Schumer went further still: “Making sure Assad knows that when he commits such despicable atrocities he will pay a price is the right thing to do.”
Unlike Rubio, who understood that viability in the coming Republican presidential contest required absolute opposition to any action by Obama, Democrats operate in a more permissive environment—at least for now. If any further proof is required of the asymmetry of the two parties, here it is.