The most constructive way for Mr. Romney to kill off his rivals while bringing the party together is simple: Steal their best ideas. Mr. Gingrich has done precisely that with Ron Paul by calling for a commission to study the gold standard. Mr. Romney could easily do the same, echoing Mr. Paul’s call for an honest dollar or adopting Mr. Gingrich’s flat tax.

He might steal a lesson in style from Rick Santorum. With little money and a shoestring organization, Mr. Santorum has managed to articulate the core arguments of the conservative agenda: why we need to address Iran, why we need to help Americans keep more of what they earn and, most of all, why the words of our Declaration of Independence and our Constitution matter still. In the last debate he proved you can be tough without being personal, skillfully demolishing all the governor’s pat answers about RomneyCare…

Those of us who believed that a primary fight would toughen Mr. Romney up have little to show for it. Far from sharpening his proposals to reach out to a GOP electorate hungry for a candidate with a bold conservative agenda, Mr. Romney has limited his new toughness to increasingly negative attacks on Mr. Gingrich’s character. It’s beginning to make what we all assumed was a weakness look much more like arrogance.