After Tuesday’s Southern primaries, Mitt Romney’s presidential campaign message can be boiled down to five words: The math is with us. It is as accurate as it is uninspiring, as much a measure of weakness as of strength. Right now, it may be the best he can offer.

It has been noted that Barack Obama used the same argument in his drive to the Democratic nomination four years ago, but the reasons the two campaigns adopted the argument are markedly different and speak to the problems of Romney’s candidacy.

By the GOP delegate numbers, Romney was the winner on Tuesday. He captured more delegates in the four contests — in Alabama, Mississippi, Hawaii and American Samoa — than Rick Santorum, Newt Gingrich or Ron Paul. He added slightly to his overall delegate lead, which remains substantial.

As they say in Boston, he was “executing against the plan.” But that plan appears to have Romney slogging forward slowly at best, rather than gaining momentum against Santorum, who is at a huge disadvantage in terms of money and infrastructure and who wasn’t considered a likely contender only a few months ago.

For Romney, victory one week is followed by defeat another. He came from behind to win in Michigan and Ohio, but the margins in both states were slim. In terms of perceptions of Romney’s candidacy, losses in Alabama and Mississippi (however narrowly, and even though he wasn’t expected to win) have trumped a few extra delegates out of Hawaii and American Samoa.

That’s partly because front-runners aren’t supposed to finish third in states where they’ve competed hard and have heavily outspent their opponents. Notwithstanding that the South is inhospitable territory for a Massachusetts Republican, the performance reinforced the reality that a sizable portion of the GOP base still hasn’t warmed to him. Does anyone think Romney looks like a stronger potential nominee today than he did on Tuesday morning?

In claiming that the math favors them, Romney’s forces are arguing inevitability as a way to divert attention from regional or demographic weakness. They’re saying that, whatever some Republicans and media critics say about his candidacy, Romney will be the nominee because neither Santorum nor anyone else can win.

All eventual nominees suffer setbacks along the way. In his primary campaign, Obama lost many states to Hillary Rodham Clinton, including general-election battlegrounds such as Ohio and Pennsylvania and solid-blue states such as New York and California. He won all of those easily in the fall. He lost the Florida primary — which didn’t count — to Clinton and kept his name off the ballot in Michigan, where he might have lost as well.

So has Romney really taken a page from Obama’s 2008 playbook? It’s understandable that some suggest he has. But the two cases are fundamentally different. Obama seized on the inevitability of the math to turn the tables on Clinton. Romney has reached for the delegate argument almost as a political lifeline.

Three big differences stand out. First, Romney is trying to defeat Santorum. That’s hardly equivalent to Obama running against Clinton. Newcomer Obama was competing with the most formidable brand in Democratic politics. Romney, who is running for a second time, is trying to put away one of the weakest fields in recent memory.

Second, Obama began his race as the underdog, not the presumed front-runner. He was attempting to upend the conventional wisdom that Clinton would be the nominee, and he used delegate math to show that it was possible. Front-runner Romney is trying to convince his party and his doubters that, whatever dissatisfaction there is with him in the GOP, he can’t lose.

Finally, Obama was a candidate who showed that he could energize the party’s base, attract supporters and generate tremendous enthusiasm. Whatever people now think of his message of hope and change, it resonated powerfully in the Democratic Party and beyond four years ago.

Romney has done little to energize the Republican base. He may be stronger than his rivals, but virtually every exit poll highlights voters’ resistance to his candidacy. Overall, his message, with its focus on the economy and his experience in the private sector, has been workmanlike but not elevating, as befits the Mr. Fix-It candidate he has tried to be.

Mike Murphy, a Republican strategist and onetime Romney adviser, tweeted this advice to Boston on Wednesday morning: “Delegate lock message is a big mistake for Romney. Dump it. Win IL, WI and beyond with voter focused message.” It’s unlikely that Romney’s team will listen to Murphy, but it would not be surprising if the candidate looks to sharpen his message on the campaign trail — and soon.

The way to think about the Republican race now was framed most cogently by Gingrich on Tuesday night. Rather than asking whether Santorum can overtake Romney in the delegate count, which seems virtually impossible, the issue may be: Will Romney still be short of the 1,144 delegates needed for the nomination by the time the primaries and caucuses end?

Romney could still reach that majority, and his team is focused on what it will require to get there. But he could fall just short, in which case he would have to spend part of the summer nailing down the last delegates he needs or even take his effort to the Republican National Convention.

Former vice president Walter F. Mondale had to find the last few delegates to secure the Democratic nomination in 1984. President Gerald R. Ford had to fight all the way to the Republican convention in 1976 to get the necessary delegates. Both lost the general election.

Delegate rules are technical and difficult to understand. There are always slight differences in the tallies of news organizations, and their delegate counts generally look far different from the figures issued by the Republican National Committee. The RNC’s count is lower than that of most news organizations because the committee does not award delegates to a candidate until those delegates are officially bound by the rules of each state’s process.

For example, the Associated Press said that, as of Wednesday morning, Romney had almost 500 delegates to about 250 for Santorum. The RNC showed Romney with about 370 delegates and Santorum with about 125.

About 900 more bound delegates will be chosen between now and the end of the primary calendar. There are unbound delegates in those contests as well. Several hundred delegates from previous contests will be bound by the time the primaries, caucuses and state conventions end in June.

Romney’s team has a strategy to nail down those delegates. Whether Santorum has a plan to stop him isn’t clear. All of that is a way of saying that Romney has a path to the majority but could be stopped short. If Gingrich remains at all viable, that could hold down Romney’s delegate totals.

But math is only part of the issue for Romney. Republicans who believe he would be their strongest nominee prefer to see him start to win consistently and with bigger margins. Counting delegates is crucial, but Romney needs to deal with larger issues to get to the magic number as quickly as possible.