That's an odd comparison considering the Iraq bit was, well, an invasion and this was an airstrike. With that in mind I would argue he is simply trying to inflame opinions against trump. I hate defending trump because I disagree with the vast majority of his agenda and proposals but this is a case where that specific criticism doesn't apply yet. Besides, the comparison perhaps will never be relevant at all. Iraq was a relatively stable country with a brutal dictator. The war was actually started by the US and after years of fighting things became bad when the US left and the iraq government was not able to hold it's position well enough. Even if the US invaded Syria, just the fact that their civil war started independently of the US would makes this into an entirely different situation. It wouldn't be "another iraq". A comparison which would make a bit of sense would be Libya but even they were never actually invaded.
I wonder if perhaps the russian response to this would be them being more aggressive in aiding Assad. Basically, a bolder russia in Syria. Of course, I doubt they would dare to directly attack the US (I am not sure if there are any US troops there, I think there aren't). but they would carry out attacks in response which they wouldn't have before against rebels. At which point we have... Basically a dick measuring contest between the US and Russia in Syria.
Edit: There are US troops at Syria. It's not implausible that they would be at greater risk as a result.
Edit: Reading on this a bit, it does not seem like trump has explained what his own endgame is. I guess his answer to that would be "I want to keep my plans a secret" though seeing how he usually is I would venture the guess that he does not have an endgame. It seems like Spicer did not even answer whether it was still a US priority to remove assad. Soooo.... the waiting game begins.