Until the last couple of weeks it was uniformly believed among conservative pundits, activists and operatives that Mitt Romney’s candidacy was dead on arrival. President Obama’s greatest liability, these conservatives were convinced, is ObamaCare. They reasoned that the base would simply never forgive Romney for championing the individual mandate plan that helped usher in RomneyCare. Conservatives, with good reason, were alarmed that, should he be nominated, the GOP would be deprived of a critical issue in the election to unseat Obama.

But then, as always happens in politics, things changed. The debate on Medicare overtook the broader debate on ObamaCare. The economy sank further. Obama got into yet another fight with Israel’s prime minister. Suddenly, it was clear that 2012 isn’t only about ObamaCare. And that’s the key to Romney’s nomination. If it’s all about “Obamneycare” (the name at least was fumbled away Monday night), he’s doomed. If it’s about a lot of other stuff plus ObamaCare and there is a divided field, Romney could pull it out.

Conservatives have rolled their eyes in disgust over Romney’s message on RomneyCare, which hinges on what is arguably a distinction without a difference outside a court of law, namely a state individual mandate vs. a national one. Conservatives aren’t buying it, but in the debate Monday night it became evident that Romney’s already running against Obama. His tripartite defense (he didn’t raid Medicare, raise taxes or institute a one-size-fits-all plan for the whole country) is really meant for the general election audience. He will have to come up with some version of: I had limited options in deep-blue Massachusetts, but as president I’ll have the latitude to do much better. It’s not ideal, but it preserves ObamaCare as an issue for the general election.

What Romney must bank on is that jobs and the debt trump all other issues. Here he can make a classic conservative vs. liberal argument as well as a competence argument against Obama.

Romney’s job in the primary is to survive without wrecking that formula for the general election. As he did in the New Hampshire debate, he’s got to seem more credible than the rest. That means conservative enough to soothe the base and stable enough to convince voters he can win in the general election and still govern from the right. As a mildly unenthusiastic Republican insider put it to me, “With Romney in the White House and a Republican House and maybe Senate I have no doubt we’d be better off.” In other words, he may be “good enough” for the primary electorate. Put Sen. Marco Rubio (R-Fla.) on the ticket and the base will be plenty excited for the general election.

But the real key to Romney’s success in the primary is to allow his opponents to slice and dice the not-Romney vote. Tim Pawlenty is attacked by Rep. Michele Bachmann (R-Minn.) on cap and trade. Pawlenty goes after Bachmann (as he has done obliquely) as an “entertainer.” Texas Gov. Rick Perry says he’s got a better record and has created more jobs than any of them. Pawlenty chides Perry for requiring all school-age girls to be vaccinated for STDs. And Romney sits back pounding away at Obama.

He’s already bagged Ames, so now Romney has to exceed expectations in Iowa where he’s trying to convince the punditocracy he’s not trying that hard. A first-place finish is a grand slam home run, a second place is a single and anything worse spells trouble. New Hampshire is a must-win, but his early, huge lead in the polls leaves him vulnerable to over-expectations. (Does a win by 5 points constitute a win or a “stumble over the finish line”?) He’s got strong support in Nevada and Michigan, but South Carolina looms large. His best bet is a replay of 2008, with him in the role of Sen. John McCain (R-Ariz.). If strong social conservatives such as Bachmann and Perry carve up the evangelical vote, Romney can slip through.

In all of this, it would seem his greatest danger is if Pawlenty becomes the consensus not-Romney choice. But unless Pawlenty can take the fight to Romney and impress donors, that won’t happen.

That Romney is still very much in the mix is an indication of how fluid the race remains. Far from being dead-in-the-water, his campaign is very much alive. There is a path to the nomination if he can forge it and if his opponents cooperate. Having weak or divided opposition is often the key to political success.