The Post’s Karen Tumulty injects some much-needed reality into the Super Tuesday post-mortem, explaining, “Though Mitt Romney’s opponents continue to insist there is a road to the Republican presidential nomination for them after the Super Tuesday contests, the arithmetic suggests otherwise.” She reports :

Even if one of [Romney’s rivals] were to begin performing far better than he has to date, it is difficult to see how he could make up the gap.

“Delegate-wise, it’s virtually impossible for Rick Santorum or Newt Gingrich to get to 1,144,” said Josh Putnam, a Davidson College professor who is an expert on the quirky rules by which Republicans in various states apportion their convention.

As I’ve noted previously, Romney will have to get by Bible Belt contests, but then he is likely to cruise through April. (“Starting in April, party rules allow states to award their delegates on a winner-take-all basis — which throws some accelerant into the process. Those will include the April 3 contests in Maryland (37 delegates), the District of Columbia (19) and Wisconsin (42). Even bigger will be April 24, when Connecticut (28 delegates), Delaware (17), New York (95), Pennsylvania (72) and Rhode Island (19) vote.”) It will pain those holding out for a brokered convention, but by April we almost certainly will see the race wrap up as Romney hits the 1,144 mark.

It is not just the delegates. Newt Gingrich has shown no ability to draw votes out of the Deep South. (He’s wise to concede Kansas and focus on next Tuesday’s contests in Alabama and Mississippi.) Rick Santorum was supposed to be the Rust Belt magnet, but it turns out he consistently repels women, urban and suburban voters and even Catholics. (Karl Rove notes: “ [Romney] nearly erased the gap among non-college graduates that’s plagued him throughout the primaries, and he once again carried Catholic voters despite the presence of Mr. Santorum, a deeply committed Catholic.”)

You can’t win the nomination, let alone the presidency, by winning only voters in the Deep South (Gingrich) or only male, committed social conservatives in rural areas (Santorum).

Moreover, the dynamic in the next couple of weeks is likely to shift from Romney to his rivals, but not in a helpful way to either of them.

Gingrich marshaled a battle plan while Santorum disclaimed (sort of) his allies’ attempts to shove Gingrich out of the race. Santorum in perfect D.C.-ese said, “I’m not saying I don’t want him to get out. If he wants to get out, I’m all for him getting out. I wish President Obama would just hand me the thing. But that’s not going to happen.” Consider how the race between today and Tuesday shifts to the two not-Romneys struggling to knock the other out. As the New York Times reported, “Advisers and allies of Mr. Gingrich said that he had no intention of quitting. Instead, Mr. Gingrich scaled back his ambitions, scrapping plans to campaign in Kansas before Saturday’s caucuses there in favor of remaining exclusively in Alabama and Mississippi during the next week.”

What about Romney? His advisers vow to keep the focus on the president, as he did in his victory speech on Tuesday. That doesn’t mean the campaign won't respond to the other candidates. However, in an effort to downgrade his opponents, Romney may very well let his aides respond to Gingrich and Santorum while he engages the president directly. Romney has shown the ability to define his opponents with ads, oppo research and earned media. Now that he’s done that spade work (in Romney’s telling, Santorum is the insider and earmarker, and Gingrich is the erratic, failed speaker), the campaign against the not-Romneys can operate almost on automatic pilot, with only minor adjustments should one of his opponents come up with something new. He can then begin framing the general-election narrative.

If Romney has his way, the rest of March will feature Santorum and Gingrich going hammer and tong, while he hopscotches between island primaries before landing in Illinois. And April, if Romney remains on track, will be when he runs the table and leaves his opponents in the dust.