HARRISBURG, Pa. — So much for Mitt Romney’s plans to compete for Democratic-trending Michigan or Pennsylvania. And what about President Barack Obama’s early hopes of fighting it out for Republican-tilting Arizona, Georgia or Texas? Forget them.

The presidential battleground map is as compact as it’s been in decades, with just nine states seeing the bulk of candidate visits, campaign ads and get-out-the-vote efforts in the hunt for the 270 Electoral College votes needed for victory. That means just a fraction of Americans will determine the outcome of the race for the White House.

“It’s difficult if not impossible to pull new states into that kind of competition,” said Tad Devine, a Democrat who long has helped his party’s presidential nominees craft state-by-state strategies to reach the magic number.

A month before Election Day, that means both candidates are concentrating their precious time and money in the handful of states that still seem to be competitive: Ohio, Florida, Nevada, Colorado, Iowa, Virginia, North Carolina, New Hampshire, and Wisconsin.

Obama succeeded in expanding the map in 2008 by winning the traditionally Republican states of Indiana, North Carolina and Virginia. But it took a Democratic tidal wave to do so, and he was the exception in a nation that’s grown increasingly polarized, with demographic shifts heralding Democratic victories in the Northeast and on the West Coast and Republican dominance in the West and South.

“Politics in the country has become homogenized regionally and culturally,” said Steve Schmidt, a veteran of Republican presidential campaigns. So, he added: “You’re left with the only states that have the population and demographic mix where it’s in question who is going to be on top at the finish line.”

TV ad money — the best measure of whether a campaign is competing in a state — shows that 93 percent of the $746 million spent so far, or $697 million — has poured into the nine battleground states. Less than a quarter of the nation’s voters live in those states.

The trend is clear. Over the past 20 years, markedly fewer states have been competitive in presidential elections. In 1992, there were 33 decided by fewer than 10 percentage points. In 2008, just 15.

Despite seemingly having the money to compete on a bigger playing field, neither Romney nor Obama is going after some states that long had been perennial swing-voting battlegrounds.

Romney hasn’t given any love to New Mexico, which now tilts Democratic because of an influx of Hispanics. And the GOP didn’t even consider competing in other traditionally Democratic states where the GOP had spent money in past presidential elections, including Minnesota, Oregon, Washington and Maine.

Obama, for his part, opted against competing in Indiana, a traditionally Republican state that’s only grown more conservative after Obama’s surprise victory there four years ago. The president also ceded Missouri; it was a presidential bellwether for years before it voted for Republican John McCain over Obama in 2008. And, unlike four years ago, there’s been no talk about trying for North Dakota or Montana.

Aides to both men had mused about waging fights on the opponent’s turf. But it hasn’t happened.

Flash back to four years ago.

With a month to go in the 2008 election, Obama and McCain were advertising and campaigning in 21 states. Obama was either trying to win — or force McCain to spend money — in GOP strongholds of Arizona, Indiana, Missouri, Montana and North Dakota. McCain was running ads in Democrat-leaning Minnesota and Pennsylvania.

And four years before that, President George W. Bush and Democratic challenger John Kerry also competed in more states than Obama and Romney are squaring off in this year. At least 11 states were the focus in the final month in a race somewhat similar to this year’s: an embattled incumbent trying to fend off a challenger.

This year, perhaps no state illustrates the changed dynamics better than Pennsylvania.

The state offers 20 Electoral College votes and has been competitive up until Election Day in every presidential campaign for the past few decades even though it’s voted Democratic since 1988.

Republican groups tried to make the state competitive for Romney this year by running ads early on.

But, one month out, Romney isn’t aggressively competing in the state, a fact that pains its Republicans.

GOP Gov. Tom Corbett was still lobbying last week, arguing that Romney’s support for relaxed restrictions on coal production made him more competitive in the state than polls suggest. That hope hung over a door in a Harrisburg campaign office in the form of a sign: “Pennsylvania believes.”

“We’ve just got to do the work on the ground,” state Republican campaign spokesman Billy Pitman said, standing beneath that hopeful sign. “There’s still time.”

But Romney has only nominally campaigned in Pennsylvania for the general election, as he struggles to narrow Obama’s advantage with white working-class voters and women. Despite Romney having 24 campaign offices in the state, registered Democrats outnumber Republicans by roughly 1 million and Obama leads solidly in polls. The president has spent a relatively light $5 million on advertising, early on in the campaign.

Then there is Michigan, Romney’s native state but one that has voted Democratic in presidential elections since 1988. GOP groups tried to lay the groundwork for Romney to compete, running ads earlier this year. But Romney aides decided against trying to put it in play, acknowledging that it would be difficult for him to win given his initial opposition to the automotive industry bailout.

On the other side, Obama’s team hasn’t put its money or time where its mouth has been in Arizona, Georgia or Texas.

Four years ago, Obama received 45 percent of the vote in McCain’s home state of Arizona without spending any time or money. This year, aides said early on that an influx of Hispanic voters made it an attractive place to compete. Obama aides say it’s still possible the president could air ads in Arizona before Election Day.

Aides also spoke early on about possibly competing in Texas, yet nothing ever came of that. And Democrats had been eyeing Georgia, arguing that it — like Southern states North Carolina and Virginia — was prime for a Democratic return to power, given an influx of young and racially diverse voters.

Yet, all those states are among the 41 that aren’t seeing the action, at least for now.

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Associated Press Kevin Freking and Don Rehill contributed from Washington.