One of the big differences is the lack of a 9/11 type of event to spur support for a response, right or wrong. There are always bad people in the world and terrorists, but there's nothing that's a single direct event that is making people see a justification for war. Iraq wasn't responsible for 9/11, but it was passable enough that it might have been for a response to the country. A war with Iraq wasn't the right response, but it was a response to something that actually happened. A war right now would just be people dying to lift Trump's ego under the false pretense of his base thinking he's somehow fighting for them, as this whole presidency has basically been anyway.