By John Whitesides
AMES, Iowa (Reuters) - No one will accuse Republican Tim Pawlenty of being too nice anymore.
Two days before an Iowa straw poll that is a critical test for his lagging presidential campaign, Pawlenty dropped his nice-guy image in Thursday's debate and sharply criticized rival Michele Bachmann for a lack of accomplishment.
Pawlenty, trailing Bachmann in Republican 2012 presidential polls and battling her for the same conservative voters, took a calculated risk that he needed to shed his mild-mannered approach and play rough if he wanted to make up ground in Iowa.
But he did not always look comfortable in the attack dog role, and several commentators panned his performance as unconvincing.
"Is she unqualified or is she just beating you in the polls?" Fox News moderator Chris Wallace asked Pawlenty.
Whether his newfound aggressiveness impressed voters will become evident on Saturday with the results of the non-binding straw poll, a mock election that is a traditional test of campaign strength in Iowa.
"He showed some backbone in taking on Bachmann, and he could get some credit for that," said Donna Hoffman of Northern Iowa University. "But I'm not sure how many minds he changed."
Pawlenty was criticized after the last debate in June for refusing to criticize front-runner Mitt Romney to his face for his support of a healthcare plan as Massachusetts governor that became a precursor to President Barack Obama's overhaul.
He later acknowledged he had flubbed the answer, and vowed he would not do it again. This time, he criticized Romney's plan and poked fun at Romney's wealth.
But he focused on taking down Bachmann, the conservative congresswoman from Minnesota who has become a Tea Party favorite and the leader in polls in Iowa, where social conservatives play a big role in the first Republican contest to find a 2012 challenger to Obama.
BACHMANN FIRES BACK
"It's an indisputable fact that her record of accomplishment and results is non-existent," Pawlenty, the former governor of Minnesota, said of Bachmann as he rattled off a list of stances she had taken in Congress and lost.
"If that's your view of effective leadership with results, please stop, because you're killing us," he said.
He made no apologies for the comments afterward.
"If you assign yourself a label of leader, you've got to be accountable for the results," Pawlenty told Fox after the debate.
Bachmann fired back at Pawlenty, saying his record in Minnesota "sounds a lot more like Barack Obama if you ask me" and describing herself as being "at the tip of the spear" in the fight against Obama.
In a sign of her status at the head of the pack in Iowa, Bachmann also was the target of a dig from former Senator Rick Santorum, another contender for the support of Iowa's social conservatives.
"You need people who are good at leadership, not showmanship," Santorum said of Bachmann, known for her flashy and outspoken style.
Romney, the leader in national polls, emerged largely unscathed from his second consecutive debate as the other seven contenders focused on each other or Obama.
Jon Huntsman, the former Utah governor who is not competing in Iowa, made his first appearance on the national stage of a presidential debate and set himself apart from the field by affirming his support for gay civil unions.
"He clearly came across as a different kind of Republican, although not one that would appeal to social conservatives in Iowa," Hoffman said. "And that's why he isn't competing here."
But the big winner of the night might have been Texas Governor Rick Perry, whose planned announcement that he will enter the race on Saturday overshadowed the debate.
Perry got plenty of headlines and publicity for his looming candidacy, and he did not have to engage in the back-and-forth with his rivals -- or even leave home in Austin.
(Editing by Eric Beech)