And it's true, strategists say, that there is little risk Portman would overshadow the presidential nominee, unlike a certain bumptious New Jersey governor.
He has foreign-policy experience as the U.S. trade representative in the George W. Bush administration, and was director of the Office of Management and Budget from June 2006 to August 2007. (This latter experience could be a downside to Portman as it would help Democrats continue their attack on Romney's policy proposals as a repeat of a failed administration.)
For his part, Portman says he was "frustrated" at some of the decisions that led to ballooning deficits at the end of the Bush years.
On the other hand, there is Ohio. If Romney can't win the quintessential swing state, it gets difficult for him to put together the 270 electoral votes required to win the White House. Portman, who has a formidable personal political organization, could help carry the crucial state - and help in Western Pennsylvania, which has similar demographics.
"I think it's very similar to Ohio," Portman said last week during an interview in Lancaster, where he was the headliner at a GOP rally.
"Eastern Ohio, in particular, is so much like Western Pennsylvania," Portman said. "It is natural gas and coal country. It is more rural, a lot of culturally conservative folks, some of whom are registered Democrats, who are going to be very interested in Gov. Romney because he's more consistent with where they are."
He said Lancaster and other GOP base counties in Pennsylvania need to generate high turnout to offset Democratic votes from Philadelphia and Pittsburgh, just as Warren, Hamilton, and Lake Counties in Ohio blunt votes from the state's large cities. "It's a familiar dynamic," Portman said.
Vice presidential candidates only rarely deliver their states for the ticket (not since LBJ helped carry Texas in 1960). Ohio could be decided by a few thousand votes either way, the thinking goes, and Portman is an asset.
The Romney team credits Portman with helping scratch out the win in Ohio's March primary over the last remaining viable challenger, former Pennsylvania Sen. Rick Santorum. Romney got his biggest plurality, about 15,000 votes, from Hamilton County, outside Cincinnati, part of the district Portman represented in the House. That's more than the 12,000-vote statewide margin of victory.
Romney's team has been tight with information on the vice presidential selection process but plans a bus tour of swing states beginning later next week that would provide a window for announcing his choice before the Republican Convention, which begins Aug. 26.
If Romney does pick Portman, he will get a guy who, though reliably conservative, has a reputation for being able to work across the aisle in Washington. He's an expert kayaker who paddled the 1,000 miles of the Rio Grande and explored China's Yangtze River. Last year, after he was upended on rapids in Chile, Portman popped his own dislocated shoulder back into place by slamming himself against a rock.
Portman's been known to come out of his house to greet the NBC producer who now shadows his every move. He is the rare politician who seems to really like reporters.
"He was on a plane with me going back to Washington last Sunday," Portman said. "And he gets on and he's in first class, because he probably flies all the time from D.C. and has plenty of miles, while I go to the back. . . . Partway through the flight, I get up to go talk to him and he's sound asleep. So I just wrote a note, saying, 'I was going to tell you whatever you wanted,' and I left it with my card on one of those little pillows."
Naturally, Portman won't talk about the vice presidential thing, and he says there are tons of qualified candidates. Besides, he said, "people are voting for the president and not the V.P."
But he's never said he's not interested in the job, either.
Contact Thomas Fitzgerald at 215-854-2718, firstname.lastname@example.org, or follow @tomfitzgerald on Twitter. Read his blog, "The Big Tent," at www.philly.com/bigtent.