In the seemingly interminable campaign for the 2012 Republican nomination, one result after another has been called “definitive” or a “breakthrough,” only for those superlatives to be dusted off again after the next round of voting.

In the seemingly interminable campaign for the 2012 Republican nomination, one result after another has been called “definitive” or a “breakthrough,” only for those superlatives to be dusted off again after the next round of voting.

But the outcome of Tuesday’s primaries in Alabama and Mississippi does seem to mark a milestone: the beginning of a two-candidate race between Mitt Romney and Rick Santorum.

True, Newt Gingrich, who finished second to Santorum in both states, says he isn’t going anywhere and even attempted to portray himself and Santorum as an anti-Romney tag team.

That doesn’t alter the fact that, based not only on Tuesday’s results but also on his earlier showings, Santorum has established himself as the “un-Romney” to whom the front-runner must pay special attention.

The result could be an edifying sharpening of the debate as Romney is forced to engage a single opponent on the issues, in the process defining himself more clearly not just for Republicans but for the general electorate.

Such a play-it-safe approach might work, even if Gingrich changed his mind and withdrew.

Romney still seems to be on what Los Angeles Times staff writer Mark Z. Barabak called “a slow, steady march to the party’s nomination,” one that in the next several weeks will pass through states more hospitable to Romney than Alabama and Mississippi were.

Why change course?

One reason is that defining his differences with Santorum might redound to Romney’s advantage in more moderate states such as Illinois and Pennsylvania.

A failure to distinguish himself from Santorum in the coming weeks could hurt Romney with voters in the fall.

With no disrespect to Gingrich or Ron Paul, the Republican race is down to two serious contenders.

Republicans aren’t the only ones who deserve to know, and in detail, how they differ.

• MCT Campus