Four days after Mitt Romney released his 2011 tax return, Vice President Joe Biden used his first in-person campaign opportunity on Tuesday to pounce: comparing Romney's effective tax rate against that of a middle-class person.

"Ladies and gentlemen, somebody today in America making $23,000 a year pays over 20-percent of their income in taxes, in some form of taxes," Biden said. "A couple making a hundred thousand dollars a year, they pay 29 percent in total tax."

"Romney paid 14 percent," Biden added, noting the Republican presidential nominee's 14.1 percent effective tax rate. The vice president proceeded to crank through the new numbers from the Friday release and also reiterated attacks that Democrats have consistently made against Romney.

"He made over $13 million dollars in income, almost all from investments which he paid in 17 percent or less," Biden said. "He got millions, he has millions stashed in tax havens like Bermuda and the Cayman Islands. The guy had a Swiss bank account. He refuses to release 10 years of his tax returns, which he demanded of his running mate?"

Biden's comments came at a campaign event in Chesterfield, Va. Though Obama won Virginia in 2008, he did not win Chesterfield County -- a suburb of Richmond and a reliably red part of the state. In 2008, Republican presidential nominee Sen. John McCain won Chesterfield County by eight points. In 2004, President Bush beat Sen. John Kerry here by 26-points.

Dispatching the vice president to the county is a clear sign the Obama campaign hopes to remain competitive.

During his speech, Biden repeatedly tailored his message to a middle class audience. In addition to comparing Romney's effective tax rate against middle class brackets, the vice president also reminded voters of the secretly recorded video in which the former Massachusetts governor said 47 percent of Americans are "dependent on government" -- and "will vote for the president no matter what."

"Look, instead of attacking folks who work for a living and pay their way, Romney should be respecting their hard work," Biden said. "That's the job of a president: to lift people up, not to tear them down."

And Biden mocked his rival.

"He, Romney? Attacking someone on taxes? I mean, whoa! That's like me attacking someone for being passionate in politics," Biden said, noting "these people pay a lot of taxes: Social Security taxes, Medicare taxes, state and local taxes, gas taxes, property taxes."

The Romney campaign was quick to respond.

"There is only one candidate in this race who has raised taxes on middle-class workers and families -- Barack Obama," spokeswoman Amanda Henneberg said in a statement.

"Governor Romney will lower tax rates across the board and eliminate all taxes on savings and investment for low- and middle-income Americans. The robust economic benefits of a lower capital gains tax rate is the reason President Clinton signed such reforms into law, and many prominent Democrats -- including members of the Obama Administration -- have supported that policy."