MoveOn ad equates Mitt Romney to Richard Nixon

(CBS News) In what may be one of the harshest ads of the 2012 campaign season yet, the liberal grassroots group MoveOn on Wednesday launched an ad that shows Mitt Romney morphing into Richard Nixon, posing the question, "Tricky Mitt: He's not a crook... right?"

The ad isn't the first time the Republican presidential candidate has been compared to President Nixon over transparency issues -- one of President Obama's top advisers recently made the comparison himself. The comparison plays into the Democrats' larger narrative that Romney is a dishonest politician who may be lying about his business record or hiding information about his taxes.

The MoveOn ad points out that Romney's record on outsourcing and his use of Cayman Island tax shelters are already matters of public debate. "So what is it Mitt Romney doesn't want us to know?" a female narrator asks, suggesting that his tax returns could contain politically damaging information or that he may have even broken the law by reporting to the government false information about his role at the private equity firm he founded, Bain Capital.

The ad is running across the key state of Ohio today in Toledo, Cincinnati, Cleveland, and Dayton. Romney, meanwhile, is holding a town hall meeting in Bowling Green, Ohio and conducting several interviews with Ohio television stations.

Recently, Romney has come under scrutiny over whether he was responsible for Bain Capital's business practices after 1999. Romney was still technically CEO of the firm at that point but says he was no longer managing the company. He's also faced pressure to release more than the two years of tax returns that he's promised to make public.

MoveOn has jumped on the opportunity to cast Romney as dishonest, having its members show up at Romney events this week with banners castigating "Tricky Mitt" for refusing to release more tax returns. In Pittsburgh and Toledo, MoveOn is flying banners over Romney's events reading, "Tricky Mitt: Release Your Returns" and "Tricky Mitt: What Are You Hiding?" The group has also joined other liberal organizations in a petition driving, collecting signatures from voters calling on Romney to release more of his tax returns.

The liberal group may be taking its cue from Mr. Obama's re-election campaign, which has run its own ads asking what Romney could be hiding. In an interview with CBS Radio News earlier this month, senior campaign adviser David Axelrod called Romney, "the most secretive candidate we've seen probably since Richard Nixon."

In response to Axelrod's comments, the Romney campaign charged that the Obama campaign was trying to distract voters from the president's record on the economy.

"With millions of Americans suffering in the Obama economy, it's no surprise that President Obama and his allies would resort to false, negative attacks in an attempt to distract Americans from the President's abysmal record," campaign spokeswoman Amanda Henneberg told CBS Radio News.