New super-PAC ad echoes Obama camp calls for Romney to release past tax returns

American Bridge posted a series of tweets Monday, including one that focuses on the 2008 presidential campaign, slamming Romney for not revealing his previous returns and directing followers to the new website. 

Speaking to Univision on Sunday in an interview at the Summit of the Americas in Colombia, President Obama said candidates for president should be "as transparent as possible."

"I think that it's important for any candidate in public office to be as transparent as possible, to let people know who we are, what we stand for,” Obama said. “And you know, I think that this is just carrying on a tradition that has existed throughout the modern presidency.” 

White House adviser David Plouffe joined the Democrats' call Friday for Romney to release more of his tax returns.

"If he's got nothing to hide, then there's nothing to lose," Plouffe said in an interview with Bloomberg TV. "I think it's a simple question of they're sitting there, they've all [been] prepared. I'm sure a lot of accountants spent a lot of time on these tax returns. Just release them."

Romney released his 2010 returns and an estimate for 2011 in February, which show he paid an effective tax rate of about 14 percent.

The presumptive GOP nominee's tax returns have been a subject of controversy on the campaign trail throughout the primary season. The American Bridge video features Romney's response to CNN moderator John King during a GOP debate in January, asking Romney if he would "follow his father's [former Michigan Gov. George Romney] example" by making returns public for more than one year.

"Maybe," he said to boos from the crowd. "I don't know how many years I'll release. I'll take a look at what our documents are and I'll release multiple years, I don't know how many years."

The Romney campaign has said the White House is trying to distract from other issues like the economy, by focusing on the tax returns.

"Gov. Romney has already released his 2010 return and an estimate of his 2011 income and taxes. He will release his full 2011 return when it is filed," Romney spokeswoman Amanda Henneberg said in a statement last week.