Sen. Rob Portman, R-Ohio, on Capitol Hill in Washington. (Associated Press)

Sen. Rob Portman has decided not to run for president in 2016, saying in a statement issued early Tuesday morning that he instead will seek reelection to the Senate.

The Ohio Republican, a seasoned politician and favorite of the GOP establishment, could have made a credible contender for the White House. But Portman said that with the new Republican majority in the Senate, he sees "a real opportunity over the next two years to break the gridlock in Washington."

"That's where I believe I can play the most constructive role," Portman said in his statement. "I don't think I can run for president and be an effective senator at the same time."

Portman said he plans to formally announce his reelection campaign for Senate in the new year. "While I appreciate the encouragement I have received from many to run for president, my focus will remain on Ohio and running for re-election to the Senate in 2016," he said.

Portman, 58, was elected to the Senate in 2010 after serving in former President George W. Bush's Cabinet, as U.S. trade representative and director of the Office of Management and Budget, and in the House for 12 years before that.

In 2012, Republican presidential nominee Mitt Romney considered Portman as his running mate and vetted the Ohioan on his short list, although Romney ultimately selected Rep. Paul Ryan (Wis.). Portman became a close political adviser to Romney and played President Obama during Romney's debate preparations.

Portman has considerable cachet within the Republican establishment. As vice chairman of the National Republican Senatorial Committee over the past two years, Portman helped recruit several star Senate challengers. Popular with major party donors, Portman raised millions of dollars for the party's Senate efforts and enhanced his national finance network. He also played an important role in bringing the 2016 Republican National Convention to Cleveland.

Portman has been considered a reliable conservative on most issues, although last year he reversed his position on same-sex marriage, which put him out of step with his party's orthodoxy. Portman decided to support same-sex marriage after his son, Will, told his parents that he was gay.

Here is Portman's statement in full:

“It’s a great honor to represent the people of Ohio in the U.S. Senate, and I have decided to run for re-election in 2016. I am excited about continuing to serve, especially with the change in the Senate leadership.

"With the new Republican majority, I see a real opportunity over the next two years to break the gridlock in Washington and actually get things done to help Ohioans and all Americans. That's where I believe I can play the most constructive role.

“I don't think I can run for president and be an effective senator at the same time.

“Over the next two years, I look forward to making progress on stalled policies to jump-start our economy, increase family paychecks, and restore the American Dream.

“Among other things, we now have the chance to fix the out-of-date, uncompetitive tax code to increase pay checks of American workers rather than encouraging companies to take their jobs overseas, cut red tape to help small businesses grow again, and stop the overreach by the Obama Administration. We can and we must export more products stamped ‘Made in America’ around the world to create better jobs and a better future here.  We must produce more American energy and use it more efficiently to lower gas prices, add jobs, and make America energy independent. And we must pass a responsible budget to address the record levels of debt.

“I plan to be active on all these issues, and others.  I know it will not be easy to break the gridlock and make Washington work, but I'm excited to roll up my sleeves to make a difference for the people of Ohio and the country.

“While I appreciate the encouragement I have received from many to run for president, my focus will remain on Ohio and running for re-election to the Senate in 2016.  I look forward to formally announcing my re-election campaign in the new year.”