there were protests, and quite large ones but they were almost exclusively from the left and were generally categorized as just being people that didn't like Bush.

Gallup polling shows 50-60% of Americans supported going in just to remove Hussein, in the first half of 2003 only 23-27% of Americans thought it was a mistake to go in to Iraq. see here for tons of polls done https://news.gallup.com/poll/1633/iraq.aspx

Despite seemingly everyone's revisionist histories, the country was scared and generally whipped into a frenzy, the right wanted it, the centrists wanted it, some of the left wanted it.