Former Massachusetts Gov. Mitt Romney and South Carolina Gov. Nikki R. Haley campaign at the Hall at Senate's End in Columbia, S.C., on Wednesday. Mr. Romney took aim at President Obama on the stump, saying he is in "over his head." (Associated Press)

Former Massachusetts Gov. Mitt Romney and South Carolina Gov. Nikki R. Haley campaign at the Hall at Senate's End in Columbia, S.C., on Wednesday. Mr. Romney took aim at President Obama on the stump, saying he is in "over his head." (Associated Press)