Portman was a U.S. congressman, trade representative and head of George W. Bush's Office of Management and Budget before he won his first term as Ohio's senator in 2010. And Quinnipiac's latest poll shows, overall, nearly twice as many voters approve of his performance as disapprove.
But nearly as many people have no opinion of Portman's performance - including a third of Republican voters.
Quinnipiac pollster Peter Brown says it's very early to ask voters to tune in.
"Average voters don't necessarily get greatly involved in campaigns until the end, and the fact that only 65 percent have an opinion about whether he deserves re-election is not really surprising."
Ohio's former Democratic governor, Ted Strickland, says he'll decide by the end of this month if he'll run against Portman. Portman's campaign committee has $5.5 million on hand.
