Davenport, Iowa (CNN) - One week before the GOP presidential candidates face off in the Iowa caucuses, Mitt Romney took the fight to Vice President Joe Biden in a speech the campaign billed as his closing argument Tuesday.
"You frankly have to feel sorry for Joe Biden," Romney told a standing-room-only audience in Davenport, where many chuckled at the mention of the gaffe-prone vice president. "I mean, four years ago he warned us about Barack Obama. Turns out he was right."
Biden dropped out of the presidential race in 2008 after disappointing caucus results.
A Romney aide said the GOP candidate was referencing a remark then-Sen. Biden made in a 2007 debate, when the moderator asked if he stood by previous comments that Obama "can be ready, but right now, I don't believe he is."
"I think I stand by that statement," Biden said in 2007, when he was still competing against Obama for the Democratic nomination.
Romney played off that admission and Biden's reputation for talkativeness Tuesday.
"Now, of course every day he has to keep quiet about that," Romney said. "You know how hard it is for Joe to keep quiet."
The attack was a shift in direction for the GOP candidate, who earlier Tuesday traded insults with Newt Gingrich in the lead-up to the Jan. 3 vote. That morning in New Hampshire, Romney mocked the organization efforts of Gingrich's campaign.
Later in the day, the former House speaker told CNN's Wolf Blitzer that Romney needed to "be man enough" to stand behind negative ads run by a super PAC supportive of Romney's candidacy.
In Davenport, Romney did not take aim at any of his GOP rivals. He fixed on Biden's Dec. 23 opinion editorial in the Des Moines Register that charged Romney's economic policies would throw America's economy into further turmoil.
"Romney appears satisfied to settle for an economy in which fewer people succeed, while the majority of Americans are left to tread water or fall behind," Biden wrote.
The GOP candidate told the audience Tuesday: "blaming others in not a plan to get America working," and directed some comments to the vice president.
"We do care that under your policies more Americans have lost their jobs, more Americans are on food stamps, and more Americans have lost their homes," he said.
Romney will spend Dec. 28 – 31 on a bus tour through Iowa.
Follow Rachel Streitfeld on Twitter at @streitfeldcnn