(CNN) - Most Americans are unfamiliar with some of the men speculated to be on Mitt Romney's list of potential running mates, according to a new CNN/ORC International Poll released Thursday.
Sen. Marco Rubio of Florida, the one person Romney has confirmed is being vetted, was the only name in the poll known by at least half of the general public.
Among those who had an opinion about Rubio, 28% said they held a favorable view of the freshman senator, while 22% said they had an unfavorable view. Another 50% said they were unsure, with 36% of those having never heard of Rubio.
Rubio, whose parents emigrated from Cuba, has been noted for his popularity among Latino voters, a crucial voting block among which Romney lags far behind President Barack Obama.
Other potential contenders include Louisiana Gov. Bobby Jindal, Sen. Rob Portman of Ohio, former Minnesota Gov. Tim Pawlenty and House Budget Committee Chairman Paul Ryan.
According to the poll, the four names had one common theme: A majority of Americans had no opinion about them, with many of them having never heard of the men.
One of the most buzzed-about names recently, Sen. Portman, especially had low name recognition.
"Nearly eight in ten are unfamiliar with Ohio Senator Rob Portman," said CNN Polling Director Keating Holland. "On the other hand, that's probably what Romney is looking for, since major party nominees rarely like to be overshadowed by their vice-presidential choices."
A popular senator from Ohio, political observers say Portman brings geographic appeal to the campaign. He also served as a budget director under the George W. Bush administration as part of a long and experienced career in Washington.
Both Louisiana Gov. Jindal and former Minnesota Gov. Pawlenty are out on the trail this week, shadowing Obama's bus tour and stumping for Romney through Ohio and Pennsylvania.
However, neither of them are particularly well known, the poll shows. Forty-three percent of Americans say they don't know about Pawlenty or Jindal.
Ryan, a congressman from Wisconsin whose name is often in headlines over his proposed budget, the so-called Ryan Plan, still does not hold much weight among Americans. Forty percent say have never heard of the House Budget chairman.
Also significant, the poll shows that when broken down by party lines, the unfamiliarity numbers don't change much, suggesting even Republicans don't know anything about the potential running mates.
For example, while 40% of all Americans have never heard of Ryan, 35% of Republicans said the same thing. Meanwhile, 40% of Republicans know nothing about Pawlenty, who ran as a GOP presidential candidate last year. And a whopping 56% of Republicans have not heard of Portman.
In addition to these men, Romney's wife, Ann, said Thursday the campaign is considering women, as well.
"We've been looking at that," Ann Romney said when asked in a CBS interview whether her husband should select a woman to join him on the GOP ticket. "I'd love that option as well. So, you know, there's a lot of people that Mitt is considering right now."
New Hampshire Sen. Kelly Ayotte, New Mexico Gov. Susana Martinez, South Carolina Gov. Nikki Haley, Oklahoma Gov. Mary Fallin, and former Secretary of State Condoleezza Rice have all been mentioned in the media as potential running mates for Romney.
The CNN poll was conducted by ORC International from June 28 to July 1, with 1,517 adult Americans questioned by telephone. The survey's overall sampling error is +/-2.5 percentage points.
– CNN Political Editor Paul Steinhauser contributed to this report.