In an interview with CNN this week in Park City, Utah, Romney discussed possible contenders in the 2016 presidential election, including Clinton, a Democrat, and New Jersey Gov. Chris Christie, U.S. Rep. Paul Ryan of Wisconsin and U.S. Sen. Rand Paul of Kentucky on the Republican side.
He said Clinton will have to answer for "the record of American foreign policy" during her term in office.
"We'll look at everything from North Korea to Iran to Pakistan, to Afghanistan, to Syria, to Egypt and you look across the world, and our prospects -- the prospects for stability, for liberal democracy, for freedom, have retreated over the period of her administration in the Department of State."
Romney said Christie has been a "very effective" governor in dealing with superstorm Sandy and working with Democrats in the state Capitol.
"You have to look at Chris and say this is a guy who's been a very effective governor and has a great potential for leadership," Romney said.
He praised Ryan, his 2012 running mate, calling the chairman of the House Budget Committee "one of the great vice presidential nominees in history," and called Paul "a very strong emerging voice in the Republican Party."
He said the three are very different from one another and the 2016 contest for the nomination will give Republicans a chance to decide "what we think the right path will be."