He has emerged as one of the most energetic cheerleaders and forceful defenders of Mr. Romney, firing back against Republican skeptics and Democratic critics alike. All but forgotten are the days when Mr. Pawlenty coined the troublemaking term “Obamneycare,” suggesting that few differences existed between the health care plans of Mr. Romney and Mr. Obama.

The conservative National Review now describes Mr. Pawlenty as “Romney’s traveling salesman.” While other potential vice-presidential candidates like Senator Rob Portman of Ohio and Gov. Bobby Jindal of Louisiana have day jobs that limit their availability, Mr. Pawlenty, who has no other full-time position, is the political equivalent of an empty nester, available to do whatever Mr. Romney asks.

“I’m happy to help where I can,” Mr. Pawlenty said in a brief interview from his home in Eagan, a suburb of Minneapolis. He deflects questions about being Mr. Romney’s partner, saying, “I think I can best serve him in other ways, but anybody would be honored to be asked.”

The vetting of possible vice-presidential candidates is approaching an end. It has been a deeply secretive process, but several Republicans close to the campaign believe Mr. Pawlenty and Mr. Portman stand out among those being considered.

In 2008, as Mr. McCain was narrowing in on a running mate, several aides recommended Mr. Pawlenty. Others pushed for a bolder choice, a candidate who would create more enthusiasm among Republican activists.

Four years later, being passed over for Sarah Palin may work in Mr. Pawlenty’s favor. “In a lot of ways, he’s the anti-Palin,” said Steve Schmidt, a strategist to Mr. McCain who expressed regret for her selection. “Here’s a guy who is prepared to be president on Day 1. In any normal year, he would have been the pick.”

But some of the same perceived shortcomings of Mr. Pawlenty still exist among his detractors, including the critique that he lacks a fiery presence and the ability to excite a crowd.

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Associates of Mr. Romney say he believes Mr. Pawlenty has gotten a bad rap, and the comfort level between the men outweighs any concerns of a potential ticket being seen as dull.

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A year ago, as the Republican presidential field was emerging, aides to Mr. Obama kept close tabs on Mr. Pawlenty and his plain-spoken message as a so-called Sam’s Club Republican. They spoke privately about how his blue-collar upbringing in South Saint Paul, Minn., in the shadows of stockyards, could be compelling to voters with the economy on their minds.

Now, as the president and his re-election campaign are relentlessly hammering away at Mr. Romney’s wealth and business background, some admirers of Mr. Pawlenty believe that he could help ease the criticism that the Republican ticket does not appeal to working-class voters.

“An appealing counterbalance to Romney being a son of a wealthy man and going to elite schools is Pawlenty being the son of a truck driver who went to the University of Minnesota,” said Ray Washburne, a Dallas businessman who began helping Mr. Romney’s campaign after Mr. Pawlenty left the race. “He’s not elite in any sense of the word.”

One thing Mr. Pawlenty may not bring to the ticket is the benefit of geography. (A key factor in Mr. Portman’s favor, Republicans believe, is the assumption that he could help them take Ohio.) But while a Republican presidential candidate has not won Minnesota since 1972, party leaders say Mr. Pawlenty is a credible messenger on the economy in swing states across the industrial Midwest.

It remains a question whether Mr. Pawlenty’s brief presidential run increased or lowered his stature as a figure in the Republican Party. His candidacy was too short to allow a thorough vetting, but there was time for him to explain some elements of his record as Minnesota governor.

He renounced his support for cap-and-trade climate change legislation, saying, “It’s fair to say I’ve had a change of position and change of view, and the reason is it’s a dumb idea.” He also received absolution from some fiscal conservatives even though he raised the cigarette tax, which he called a “health impact fee.”

Grover G. Norquist, who leads the group Americans for Tax Reform, said the full scope of Mr. Pawlenty’s record was strong, despite the tax increase. He pointed to his leadership on a 44-day transit strike in 2004, where he won a fight over compensation and retirement benefits.

“He was a little Scott Walker before Scott Walker,” Mr. Norquist said, referring to the Wisconsin governor hailed among conservatives for surviving a recall election last month after cutting collective bargaining rights for most public workers.

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While Mr. Pawlenty left the Republican primary long before voters weighed in, he won an early poll of evangelical Christian leaders, a constituency Mr. Romney has had difficulty winning over. His longtime pastor, Leith Anderson, who is also president of the National Association of Evangelicals, said Mr. Pawlenty’s faith could help the Republican ticket.

“Tim Pawlenty is an evangelical, and evangelicals like other evangelicals,” Mr. Anderson said.

Mr. Pawlenty, who joined several corporate boards and is looking for other private sector opportunities after nearly two decades as a legislator and governor, has gradually adjusted his posture on a vice-presidential candidacy. In April, he told Fox News, “I’ve taken my name off the list.”

A month later, after he received a call, his friends believe, from Mr. Romney, he said he would be honored to be selected.