the saudi campaign, and i have to know that to be able to assess the likelihood of success. >> reporter: the u.s. military involvement, as sensitive as it gets. saudi arabia is backing beleaguered yemeni president hadi who has fled his country. the rebels are backed by iran. the u.s. worries terror groups will exploit the chaos. >> there's a lot at stake here, particularly with al qaeda and isis both active in yemen. but let's face the facts. the u.s. is involved now in a proxy war between the saudis and the iranians. >> reporter: iran condemning the intervention. >> it is a very dangerous situation. we believe any interference in yemen will simply lead to further loss of life. >> reporter: barbara starr, cnn, the pentagon. >> for more insight and analysis, let's bring in