True that Congress should have been presented the evidence and given the go ahead. And that could have happened very quickly, because it has a lot of support on both sides of the aisle.

However, the Iraq experience is a false analogy. The Bush administration WANTED desperately to depose Saddam, so they cooked the intel to support it. Trump wanted to stop opposing Assad and leave him in place. Changing to the attack posture meant this had to change drastically which is rather embarrassing and goes against Trump's affinity for Putin. If anything, the current administration would cook the intel to say it was somebody else. But they didn't.

Probably because the intel is satellite video of the Syrian air force loading the gas bombs onto the planes, flying to the delivery site, and dropping the bombs.