Biden's jabs mark a major escalation in Obama's reelection campaign and refocus his political team on Romney, whom Obama advisers have long considered his most likely opponent. It switches Obama away from his just-concluded tax-cut victory over House Republicans to the GOP presidential field just days before the Iowa caucuses.
"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 Obama team may be betting on Romney, but his Republican rivals were conceding no such ground.
Campaigning in South Carolina, former House Speaker Newt Gingrich derided Romney as a "Massachusetts moderate trying to come down and pretend to be a conservative. But I'm not going to say anything stronger than that. I'm going to focus on positive things."
Asked later how that wasn't being negative, Gingrich said: "I didn't criticize him. I described him accurately."
And he swiped at fellow candidate Rep. Ron Paul of Texas for wanting to shut overseas military bases, a stark departure from the Republican mainstream and one not bound to sit well in pro-military South Carolina.
"The only person I know who is for a weaker military than Barack Obama is Ron Paul," Gingrich told 300 people outside a Columbia restaurant. "If we become isolationist, the world would become a more dangerous place overnight."
Rep. Michele Bachmann's campaign said she would start radio and TV commercials in Iowa, her first since her straw poll victory in the state in August. In them, she stresses her Christian values and that she's "an Iowa girl from Waterloo."
Also Friday, the Republican Party of Virginia said Texas Gov. Rick Perry's campaign had failed to gather the required 10,000 signatures of registered voters needed to put his name on the ballot for Virginia's March 6 presidential primary.
Biden's words summed up a running story line about Romney that Obama's campaign and the Democratic Party have been refining for months. The piece also was a direct rebuttal to Romney's recent assertion that he wants "an opportunity society" versus what he called Obama's "entitlement society."
Biden reiterated a major theme of Obama's reelection effort, one the president spelled out in a recent speech in Kansas in which he declared that the middle class was at a make-or-break moment. In taking on Romney, Biden defined "opportunity" in his own terms.
"We believe deeply in opportunity - that if you work hard and play by the rules, no opportunity should be out of reach," he wrote. "This is a fundamentally different vision than what the other side has proposed."
Romney, speaking at the Tilt'n Diner, quickly countered that it was Obama who was hurting the country and expressed astonishment that Biden would have the "chutzpah . . . the delusion" to write such a piece.
"They need to get out to diners like this," he said.