the caption, "isn't this ridiculous?" the tax issue bedeviled romney in the 2012 campaign after democratic senate leader harry what romney is now saying about trump. >> the word's out that he hasn't paid any taxes for 10 years. let him prove that he has paid taxes, because he hasn't. >> reporter: the accusation was later debunked. for his part, trump has boasted he tries to keep his tax bill low. >> i fight like hell not to pay taxes. i hate the way the government spends my money. >> reporter: and he noted on twitter that, "tax returns have zero to do with someone's net worth." romney's response, "me thinks the conald doth protest too much." trump's g.o.p. rivals marco rubio and ted cruz have both pledged to release their returns. >> they're not very exotic, but we will release them. >> i haven't made enough money that my tax returns are interesting. >> reporter: donald trump is on a three-state winning street and won 60% of the delegates awarded so far. tuesday presents the...