Mitt Romney might have silenced the “anyone but Romney” critics in the Republican Party for now, with his big win in the New Hampshire primary. But watching the former Massachusetts governor’s victory speech last night it struck me that he remains vulnerable.

He is vulnerable on the very territory that he again defined as the battleground in the fight with President Obama: jobs and the free market. And it is his own fault.

Romney’s remarks in Nashua were worse than a gaffe. It was not a slip of the tongue when he said, “I like being able to fire people who provide services to me.” It was a deliberate choice of words and he enjoyed saying it. He clearly did not realize that he had handed a gift not only to his five Republican rivals but also to Obama. Although taken out of context (he was referring to the freedom to switch health insurance) this is a talking point that will run and run.

Since Monday, there has been increased scrutiny in the media and in the Republican Party on Romney’s corporate credentials. Doubts have been cast on his claim that he created 100,000 jobs in the private sector. His record at Bain Capital is being examined. Former House Speaker Newt Gingrich, who was the first to accuse Romney of building his career by sacrificing his employees, is now heading to South Carolina with a 27-minute attack documentary on the “corporate raider.”

Romney was probably right when he said last night that the criticism from both the Obama camp and the unnamed “desperate Republicans” aligned with the president smacks of “resentment of success.” This is a new phenomenon, but it has been exploited by the Occupy Wall Street movement, which identifies Romney as a member of the 1 percent.

So Romney should not rest easily on his New Hampshire laurels. None of his five rivals abandoned their campaign last night. It’s on to South Carolina and the Jan. 21 primary. The front-runner might have grounds to fear the return of “anyone but Romney” whispers from stage-left.