CHARLESTON, S.C. -- Sen. Rob Portman, a rising Republican star in Washington who is seen as a potential vice presidential candidate, is endorsing Mitt Romney for president and plans to campaign with him here on Thursday.

Portman, who represents the critical swing state of Ohio and served as President George W. Bush's budget director and trade representative, praised Romney in a statement as "the one candidate who will be able to defeat President Obama in November and bring conservative change to Washington."
"Four years ago, President Obama came to Ohio and promised to change the broken system in Washington and fix our economy - he has failed on both counts,” Portman said in a statement to be released by the Romney campaign. "Mitt Romney has been a lifelong leader who has shown how to bring people together to turn around tough situations.  And right now, that's exactly what our nation needs. Americans can be proud to stand behind Mitt -- he has balanced budgets, cut taxes, and created jobs."
Portman plans to campaign with Romney in South Carolina on Thursday in advance of the evening's CNN Republican primary debate.

Other top Romney surrogates, including former Minnesota and New Hampshire governors Tim Pawlenty and John Sununu, as well as South Carolina Gov. Nikki Haley, will join Romney here in the final days before Saturday's South Carolina primary, according to a campaign aide.
Before joining the Bush Administration, Portman served in the House, including under then-speaker Newt Gingrich, one of Romney's rivals for the presidential nomination.

Portman in a statement to supporters that he had not planned to endorse so early in the primary process.
"However, I feel one candidate's policy positions, debate performances, and character make him the best candidate to take on President Obama, and I feel our chances in November will be improved by coalescing around one candidate and stopping the political attacks among Republicans," Portman said.
Romney, in a statement released by his campaign, said that "it is an honor to have the support of such a committed public servant."
“Bringing fiscal sanity to Washington is critical for our country’s future economic health and national security," Romney said. "In the United States Senate, Senator Portman has been a leader in the fight for a balanced budget and I look forward to working with him to make the federal government simpler, smaller, and smarter.”