Washington (CNN) - His name is bantered about all the time in the media as a potential running mate for Mitt Romney, but a new poll indicates that more than half of Americans don't know enough about Rob Portman to form an opinion of the Republican senator from Ohio.
According to an ABC News/Washington Post poll, 51% of the public says they have no opinion of Portman, a former cabinet official in George W. Bush's White House and former congressman. While high, that's lower than the 81% who said in a CNN/ORC International poll in mid-April they didn't know enough about Portman to form an opinion. Since then Portman's become more visible on the campaign trail as a Romney surrogate and has appeared more in the media.
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Nineteen percent of those questioned in the new survey say they have a favorable impression of Portman, with three in ten saying they see him in an unfavorable light.
Even among just Republicans, voters are divided, with Portman having a 21%-22% favorable-unfavorable rate.
Sen. Marco Rubio of Florida, whose name also comes up as a possible running mate for Romney, the presumptive GOP nominee, is a bit better known nationwide. According to the poll, 39% say they don't know enough about the freshman senator to form an opinion. Thirty-two percent say they have a favorable impression of Rubio, with 29% saying they see him in a negative light. Among Republicans only, Rubio has a 46%-14% favorable-unfavorable rating.
Portman's and Rubio's low name recognition nationally is nothing new for potential running mates, who in past cycles have also often not had strong profiles.
Former Gov. Jeb Bush of Florida is much better known, thanks to his years in office and his family connection to his father and brother, both former presidents. Only 19% say they don't know enough about him to form an opinion. Among all Americans, the poll indicates 36% have a favorable view of Bush with 45% holding an unfavorable rating. Among Republicans only, Bush has a 63%-19% favorable-unfavorable rating. Asked about being a running mate, Bush told CNN last Friday that "I won't do it."
The ABC News/Washington Post poll was conducted May 30-June 3, with 1,009 adults nationwide questioned by telephone. The survey's overall sampling error is plus or minus 3.5 percentage points.