In his most high-profile speech before a nationwide audience, a feisty Tim Pawlenty told thousands of cheering Republicans on Wednesday they were celebrating at "Barack Obama's retirement party."

The former Minnesota governor took some of the harshest jabs at President Obama at the Republican National Convention, saying: "Like a big tattoo, it seemed cool when you were young."

Later on, "that decision doesn't look so good, and you wonder: what was I thinking? But the worst part is you're still going to have to explain it to your kids."

Pawlenty has emerged as one of the most devoted surrogates for Romney, crisscrossing the nation to build enthusiasm and excitement for the former Massachusetts governor. The Romney campaign tapped Pawlenty for a prime speaking slot on the run-up to what was expected to be a rousing introduction of Romney's running mate, Wisconsin Rep. Paul Ryan.

Rather than building on a vision of America laid out by other speakers, Pawlenty took on the role of attack dog.

"Ah, the Obama White House, one bad decision follows another," Pawlenty said. "Hard to say exactly just what his worst mistake has been. There's so many to choose from: The stimulus. His energy policy. Obamacare. Taxes. Joe Biden."

Pawlenty framed the Obama as a do-nothing president who has only created jobs for golf caddies and is always passing off blame for the nation's ills.

"It's the bank's fault. It's Europe's fault. It's the weather's fault. It's Congress' fault," Pawlenty said. "Barack Obama's failed us. But look, it's understandable. A lot of people fail at their first job."

After a string of blows to the president, Pawlenty said Obama doesn't understand the problems of entrepreneurs.

"They're collectively making one common plea," Pawlenty said. "They're saying: 'I want to grow my business and employ people, but they're also saying this: Just get the government off my back.'"

Pawlenty said these people need help, "and help's name is Mitt Romney."

Pawlenty touted Romney's success resurrecting failing companies, salvaging the Winter Olympics and governing Massachusetts.

"When he sees a problem, he goes after it and finds the solution," he said. "It's that can-do spirit, combined with a lifetime of service and success that convinced me to support him. And it's that can-do spirit that we need in the White House, leading America now."

Pawlenty's speech came about an hour after the Maine delegation, which strongly backed Texas Rep. Ron Paul for president, marched around the perimeter of the arena, chanting "so goes Maine, so goes the nation," and then left through the front doors.