"The public ought to know that," Clinton said. "The voters can make up their own mind whether they think it's a good thing for a person who wants to be president to minimize his own tax liability by putting the money in overseas tax shelters."
Clinton piled on Friday, suggesting it is unusual and breaks with tradition for Romney to hold back.
"It's the first time in, I don't know, more than 30 years that anybody running for president has only done that," he said.
Clinton noted that Sen. John McCain (R-Ariz.), the 2008 Republican nominee for president, released more. Clinton said he thought McCain released some 20 years' worth, but it was actually Democratic nominee John Kerry who did that in 2004. McCain released two years of tax returns when he was the Republican nominee, and he has defended Romney's decision to release one year.
"Two years is sufficient,” McCain told CBS’s “Face the Nation."
Romney also released an estimate of his 2011 return, and filed for an extension that lasts until October.
"All the taxes are paid, as appropriate. All of them have been reported to the government. There's nothing hidden there," Romney told Radio Iowa on Tuesday.
Clinton also defended the president's campaign for going after Romney's record as governor of Massachusetts and as the CEO of Bain Capital.
"It's just as relevant as going over my record as governor when I ran for president," Clinton said. Clinton was the governor of Arkansas prior to running for president.
"[Romney's] put it at the forefront; he's said, basically, 'I'd be a better president because I know how to create jobs, because that's what I did,' " Clinton continued, using essentially the same reasoning that Obama's campaign has. "All your work life before you run for president is relevant."