The latest addition to the pool of potential Republican presidential candidates may not have national name recognition, but he has experience playing the part.

Sen. Rob Portman, who kicked off his would-be campaign with a visit to New Hampshire Tuesday, has played the role of the Democratic candidate during debate prep sessions for the last three Republican presidential nominees.

The Ohio Republican was also on the short list of potential running mates for Mitt Romney in 2012.

Republicans close to Portman say his decision to test the waters in New Hampshire was part of a very serious, deliberate consideration of whether to run for the White House in 2016.

As vice chairman of the National Republican Senatorial Committee, Portman is in charge of fundraising. Advisers say that will keep his focus on helping the GOP win control of the Senate — off the White House — until after the November midterms.

“He’s an adult, he’s got some experience; he also has a billion dollar Rolodex. He’s the only person who has walked through Bush World, McCain World and Romney World,” said Republican consultant Barry Bennett, Portman’s top political advisor. “If you’re a generous donor, he’s probably been to your house. That’s obviously is a huge deal to string together the money to run a campaign.”

In New Hampshire, host of the nation’s first presidential primary and second nominating contest, Portman was the featured guest at “Politics and Eggs,” a traditional stop for prospective presidential candidates. He visited the Nashua office of the state GOP, and logged some volunteer time making calls from the party’s phone bank. Later in the day, Portman headlined an event for Senate candidate Scott Brown as a part of his role as NRSC vice chairman.

Portman’s NRSC post has provided him with a fresh opportunity to expand an already solid fundraising network. It also gives him a pretense to travel to some key early primary states. In addition to New Hampshire, the GOP is competing to flip a Democratic-held seat in Iowa, whose nominating caucuses kicks off the presidential primary season.

“I want to be part of the conversation in the fact that the country is in trouble and we need to make some changes. If we don’t we will continue to slip back behind other countries,” Portman said in typical understated fashion, when asked about his presidential aspirations during an interview with New Hampshire political reporter James Pindell of WMUR television.

For now, Portman’s presidential kitchen cabinet is small.

It’s basically Bennett, who has been advising Portman since his first run for Congress in 1993. Bennett is a partner at the GOP firm BKM Strategies, whose other two principles include Kara Ahern and Mary Cheney, the daughter of former Vice President Dick Cheney.

Portman also has an extensive political network dating back to his service as an appointee for President George H.W. Bush. He has functioned as a top fundraiser and adviser to the three most recent GOP presidential nominees: President George W. Bush; Sen. John McCain, R-Ariz., and Romney. And he comes from Cincinnati, a major stop on the Republican fundraising circuit.

The senator would have a wealth of relationships with influential establishment Republican players to draw from should he run for president. Conversations with those individuals have begun, GOP sources say.

“There’s an informal network of both national Republicans and early state Republicans that he’s talking to,” a GOP insider said.

Portman has extensive Washington experience, having served in multiple roles in two White Houses. He served for a dozen years in the House and won election to the Senate in 2010. Despite the focus on the supposed advantage of hard-edged conservatives in GOP presidential primaries, the pragmatic candidate with a broader appeal tends to win the party’s nomination.

Portman supporters say the senator would fill that political space in what is expected to be a crowded field, and believe he as a “viable” path to victory. They also say his Midwestern roots could play well in a party looking to reconnect with middle-class voters four years after President Obama successfully demonized the GOP nominee as out of touch with average Americans.

The knock on Portman, a soft-spoken dealmaker, is that he is too straight-laced to connect with voters on an emotional level. His public support for legalized same-sex marriage also is a liability, as is, potentially, his service under President George W. Bush.

“Portman is vanilla without the vanilla part. Makes vanilla look flavorful,” said a Republican operative supporting another potential 2016 candidate. “The other problem I think he’s going to have is that he’s incredibly uncomfortable with any party of the Republican philosophy except dollars and cents. Donors love that kind of Republican but they always struggle with primary voters.”