Mitt Romney does not have to win Ohio to win the presidency, Sen. Rob Portman (R-Ohio), a top surrogate to the Republican presidential nominee said Sunday morning. 

Sen. Rob Portman (R-Ohio), left, and Republican presidential candidate Mitt Romney. (Charles Dharapak/AP)

“Look, he can probably win the presidency without Ohio, but I wouldn't want to take the risk,” Portman said on ABC News’s “This Week With George Stephanopoulos.”

As Portman noted, no Republican has won the presidency without carrying the state of Ohio, a prize which brings with it 18 electoral votes this year.

“We're doing great in Ohio. If you look at the average of all the polls, it's about dead-even in Ohio right now. And importantly, the momentum's on our side. It's been terrific,” Portman said.

Romney and President Obama will meet Tuesday night in their second debate. Portman has been playing the role of Obama in Romney's debate preparation sessions.