AMES, Iowa – GOP presidential front-runner Mitt Romney and seven rivals trying to emerge from the pack castigated President Barack Obama’s handling of the economy and the debt ceiling debate Thursday night in a debate shadowed by the latest Republican to join the field, Texas Gov. Rick Perry.

“I’m not going to eat Barack Obama’s dog food,” Romney said when asked whether he would have vetoed the compromise legislation that Congress gave to the president that raised the debt ceiling. “What he served up is not what I would have as president of the United States.”

Tim Pawlenty, the former Minnesota governor, assailed Obama for “his lousy leadership and lousy economy.” And Rep. Michele Bachmann noted that she had voted against raising the debt ceiling. She raised her voice saying she had a message for Obama: “You are finished in 2012, and you will be a one-term president.”

Minutes later the two Minnesota rivals attacked each other’s records, underscoring how much each has on the line in a test vote in Iowa on Saturday that could make or break their candidacies.

Pawlenty, who is struggling to gain traction, went on the offensive, accusing Bachmann of achieving nothing significant in Congress, lacking executive experience and having a history of fabrications.

“She’s got a record of misstating and making false statements,” Pawlenty said.

Bachmann, who has risen in polls since entering the race this summer and has eclipsed Pawlenty, responded with a list of what she called Pawlenty’s liberal policies as governor, including his support for legislation to curb emissions.

“You said the era of small government is over,” she told Pawlenty. “That sounds a lot like Barack Obama if you ask me.”

Notably absent from the stage were Perry, who was in Texas, and former Alaska Gov. Sarah Palin, who isn’t a candidate but was stoking presidential speculation anew with a visit to the Iowa State Fair.

Just hours before the start of the eight-candidate spectacle, Perry’s aides made it known that he was running for the GOP nomination. Texas’ longest-serving governor was finalizing plans for a weekend announcement tour. It was the latest twist in the most consequential week yet in the 2012 Republican presidential nomination fight.

Capping it all, along with Perry’s announcement, will be Saturday’s Iowa straw poll. It’s an early test of strength for Republicans competing in the state and could well winnow the field.

The nation’s teetering economic situation shadowed the debate, with stock market volatility and a downgrade in the nation’s credit rating giving Republicans ample opportunities to criticize Obama.

The Democratic president will get his shot to counter the criticism next week during a Midwestern bus tour that will take him through this state that helped launch him on the path to the White House four years ago.

For now, however, the Republicans commanded the spotlight, with seven candidates seeking to separate themselves from the packed field and emerge as the chief alternative to Romney.

Pawlenty, who hesitated in a June debate to criticize the former Massachusetts governor, poked at Romney and Obama at the same time.

“Where’s Barack Obama on these issues. You can’t find his plans on the most pressing issues in this country,” Pawlenty said, promising audience members and TV viewers he would “come to your house and cook you dinner” if they could find Obama’s proposals. “Or if you prefer I’ll come to your house and mow your lawn. … In case Mitt wins, I’d limit it to one acre.”