happens and reporting it if it's suspicious, reporting what you hear. >> reporter: sanders, standing firm on his view, that the u.s. should not send troops overseas to fight isis. >> to tell saudi arabia that instead of going to war in yemen, they, one of the wealthiest on earth have to tell qatar instead of spending $2 billion on the world cup, maybe they should say attention to isis which is at their doorstep. >> martin o'malley taking on his democrats on training and gun control. >> the easiest way to buy a combat assault weapon is at a gun show and because of the flip-flopping political approach of washington that both of my two colleagues on this stage have represented there. >> whoa. >> reporter: but all three candidates zeroing in on a presidential hopeful who wasn't on stage. donald trump.