Results show a large dip in approval of the Iraq war in comparison to the previous time the pollsters asked if the war had been worthwhile. In 2013, 59 percent said the Iraq war wasn't worth it, while 35 percent said the opposite.

The criticism of the Iraq war runs across all ages. Just 23 percent of young adults and 21 percent of seniors think the war was worthwhile. Support was also low among men — only 22 percent answered that the war was worth it.

When it comes to U.S. intervention into Iraq to stop militants from taking over the country, Americans are divided. Half say the U.S. does not have a responsibility to intervene and 43 percent answered that the U.S. has an obligation to help.