There’s not much that the campaigns of Barack Obama and Mitt Romney agree upon these days, except for this: The 2012 presidential election remains to be won or lost in the next 16 days because neither side has been able to close the deal with voters.

Close to three-quarters of a billion dollars in advertising — more than 80 percent of it negative — has flooded the airwaves of the battleground states. Legions of volunteers have spent tens of thousands of hours making phone calls and knocking on doors. There have been two conventions and three debates.

And yet, as the presidential race heads into this final stretch, it is ending up pretty much where it started — exceedingly tight.

So what has to be accomplished in these last two weeks? Both campaigns also agree on that.

“What we’ve got to do is two things and two things only: persuade the undecided, and turn our voters out,” Obama campaign manager Jim Messina said. “We have a strategic advantage in size and footprint on the ground — and, even more importantly, in experience.”

Explore the 2012 electoral map and view historical results and demographics

Those in Romney’s camp, however, insist that their ground operation will not be outdone as John McCain’s was four years ago. Theirs, they say, is more like the superior one that George W. Bush ran in 2004 — and with technological advantages that weren’t available then, which will keep them nimble until the end.

“The quality and quantity of the data is light-years ahead of where we’ve ever been,” said Rich Beeson, Romney’s political director. “So we’re going to be able to make a lot of informed decisions in this last two weeks that we’ve never been able to make before, because we didn’t have the ability to see what we can now see.”

That kind of chest-thumping is typical of the psychological warfare that comes at the end of a tough political campaign.

But there are also tangible ways to assess the end game.

Early voting is underway in many of the swing states, and absentee ballots are out in all of them. The two campaigns are combing the data on both for patterns that will show how well they are doing, as well as where they need to step up their efforts.

And more revealing than their shadow boxing is how and where the two campaigns are choosing to spend their most precious resources of time and cash.

The map

The battlefield this year is a narrow one. In fewer than a dozen states is the outcome in serious question. More than $350 million has been spent on television advertising in the biggest prizes: Florida, Ohio and Virginia.

When the Romney campaign announced last week that it would begin shifting staff out of North Carolina, it was a declaration of victory in the state once considered so up-for-grabs that the Democrats decided to hold their convention there.

“It’s baked,” said one top Romney strategist, who spoke on the condition of anonymity to discuss campaign strategy.

Romney’s team also claims that narrowing polls suggest there may be opportunities in some states that were thought to be a lock for Obama, such as Minnesota and Michigan. And GOP vice-presidential nominee Paul Ryan scheduled a stop on Saturday in Pennsylvania — a state where registered Democrats outnumber Republicans by 1 million.

Obama campaign officials, of course, dispute that, and note that Romney is not spending money on advertising in those states.

“We continue to have more pathways to 270 electoral votes than they do,” Messina said. “All of our pathways are still there.“

The president’s frenetic campaign schedule this week reinforces that contention. On Wednesday, he will launch a two-day, round-the-clock sweep through Iowa, Colorado, Nevada, Florida and Virginia, after which he will return home to Chicago to vote early. And on the way, Obama will call undecided voters from Air Force One.

Meanwhile, Obama’s team is increasingly confident of its prospects in Nevada, another swing state.

The state has the highest unemployment and foreclosure rates in the country, which might have made it more receptive to Romney. But Nevada has seen enormous growth in its Latino population, which polls suggest will vote overwhelmingly for Obama. The president also stands to benefit from the reach of Senate Majority Leader Harry M. Reid’s organization there and from the disarray of the state GOP.

The message

Romney’s and Obama’s closing arguments are beginning to take shape.

Although Obama was largely hailed as the winner of last week’s raucous presidential debate in New York, Romney’s team was getting another message from a focus group of undecided voters who watched from Cleveland.

Women in particular, campaign officials said, found Romney to be more “commanding” and scored him higher on the question of which candidate “has a plan to get the country back on track.”

Few voters are undecided at this point, both campaigns say, and a majority of those are women, a group with which Democrats normally have a big advantage. But a number of polls since the first debate have suggested that Romney is gaining ground with female voters, particularly white suburban ones.

It is with an eye to voters such as these that the Romney campaign has recently retooled the former Massachusetts governor’s stump speech. Where he once roamed the stage with a hand-held microphone, he now stations himself, more presidentially, behind a lectern.

He talks less about how Obama has failed — a recognition of the fact the voters are growing more optimistic about their economic prospects as unemployment rates edge downward — and argues instead that pro-business policies would bring about a more robust recovery.

Obama, on the other hand, has honed a sharper edge. On Friday, at a rally in Virginia, the president mocked Romney’s efforts to reposition himself toward the center as “Romnesia.”

“Now that we’re 18 days out from the election, ‘Mr. Severely Conservative’ wants you to think he was severely kidding about everything he said over the last year,” Obama said.

And a tough new Obama television commercial in Ohio ends with the tagline: “Mitt Romney. Not one of us.”

After Monday night’s final debate, there will be little persuading left to do. So the campaigns will turn almost all their energies to the unglamorous grind of making sure every supporter they can find casts a vote.

Getting out the vote

Democrats note that they have more registered voters than Republicans do in five of the most intensely contested states: Florida, Iowa, North Carolina, Nevada and Pennsylvania. Republicans hold an edge in Colorado and New Hampshire. And in three battleground states — Ohio, Virginia and Wisconsin — voters do not affiliate with a party.

Democrats have also done a better job of registering new voters, although Obama strategists note that they still have to make sure they show up at the polls.

By the time Election Day arrives on Nov. 6, it is expected that more than one-third of voters will have already cast their ballots.

Early voting was a critical factor in Obama’s victory four years ago. In at least four states — Colorado, Florida, Iowa and North Carolina — he had such a lead built up that he won despite losing among those who waited until Election Day to vote, according to an analysis by the Associated Press.

Romney’s campaign is determined not to let that happen again and says it is narrowing Obama’s early-voting advantage in some states.

In Iowa, for instance, Romney strategists think that Obama will have to have a 100,000-vote lead from early and absentee voting to win against a GOP surge on Election Day. “Right now, they’re not on pace to do that,” Beeson said.

Both campaigns put out memos last week claiming an advantage among early voters in Ohio. But it is hard to tell which is right, considering that Romney’s figures are based on presumptions about absentee-ballot requests in a state where voters do not register by party and Obama’s are based on public polls of those who have voted early and absentee.

Michael McDonald, a George Mason University professor who studies voting trends, looked at the data and determined that while Democrats have an early-voting advantage in Ohio, the Republicans are not being caught off-guard, as they were four years ago.

“Looking across the Ohio counties, it appears that early voting is up everywhere across the state,” he wrote last week in the Huffington Post. “Both campaigns are hard at work through the extended early voting period.”

Still, no one disputes that Obama — who did not have a primary to contend with — got a much earlier start on his ground operation and has built a far more extensive infrastructure. For instance, his campaign opened its office in Chillicothe, Ohio, late last year — nine months earlier in the cycle than it did in 2008.

“Are they better organized than John McCain? Probably,” said Jeremy Bird, Obama’s field director. “Are we better organized than we were in 2008? I’m sure of it.”

Amy Gardner and Philip Rucker contributed to this report.