WASHINGTON — The Obama election campaign has a politically loaded question it wants voters to think about: What is Mitt Romney hiding?

Not a thing, Romney maintains. The Democrats are just trying to change the subject from the weak economy.

It’s a newly intense back-and-forth as President Barack Obama’s campaign team tries to cast his Republican opponent as a secretive rich guy who keeps his money in offshore accounts and refuses to release more of his tax returns.

The coordinated push, which includes stinging criticism from Obama and Vice President Joe Biden, Web videos and television advertisements, comes as the Democrats grasp for ways to gain an advantage.

Getting personal, Biden declared Tuesday that Romney was “making a lie of the old adage, like father, like son” by not meeting the standards his father, George Romney, set when he released 12 years of tax returns during his 1968 presidential bid. In a speech to Hispanic leaders in Las Vegas, Biden said of Romney: “He wants you to show your papers, but he won’t show us his.”

The Obama campaign posted a video on YouTube Tuesday that asked: “How long can Romney keep information on his investments in overseas tax havens secret? And why did he do it in the first place?”

Romney aides have called the barrage of attacks an “unfounded character assault” by a campaign desperate to distract attention from a sluggish economy. And Romney insists his private financial records contain nothing illegal.

“I have followed the law,” Romney said Tuesday on Sean Hannity’s radio show. “I have paid my taxes as due. I have also disclosed through all of the requirements of the government, every asset which I own, fairly and honestly, recognizing, of course, not to do so would be not only wrong but illegal and criminal.”

Still, Romney has released only a single year’s federal return — for 2010 — along with an estimate for 2011. Other returns could contain information about accounts he has held in Switzerland, the Cayman Islands and Bermuda, and that has created an opening for Democrats to accuse him of being secretive and taking advantage of tax loopholes that aren’t available to average Americans.