Mr. Romney showed he knows how to take an opponent down; now he needs to show the ability to build himself and the rationale for his candidacy up. He should become bolder in his prescriptions, presenting a confident agenda for economic growth and renewed prosperity through reforms of tax, regulatory and energy policies.

There’s no reason he can’t, or shouldn’t do so. While Mr. Gingrich called Congressman Paul Ryan’s entitlement reforms “right-wing social engineering,” Mr. Romney complimented them last November. He can refresh that speech and give it again. He can also build on his best moments in recent debates, when he unapologetically and passionately defended free enterprise. Far better to best Mr. Gingrich in the weeks ahead by taking the fight to President Obama, challenging the incumbent’s unpleasant attempt to appeal to envy and resentment.

If he does these things, Mr. Romney will improve his chances of consolidating Republicans and winning the nomination battle earlier and in better shape for the fall. If not, the GOP contest will go on, the bitterness will linger, and the road ahead could be treacherous.