Despite an apparent poll bounce for Mitt Romney in recent weeks, the fundamental dynamic of the presidential electoral map appears to be locked in, with the two campaigns focused on the same nine states that have dominated for most of the year, according to strategists on both sides.

The Republican nominee has enjoyed some momentum after his winning performance in the first presidential debate, which has seemingly put once-written-off states such as Pennsylvania and Michigan back in the mix, according to polls out this week. But the Romney campaign appears to be resisting pressure from supporters to broaden the fight and, at least for now, is not expanding its path to the 270 electoral college votes needed to capture the White House.

That leaves Romney with a very narrow road to victory, one that probably requires him to win large battlegrounds such as Florida, Virginia and Colorado along with Ohio, a swing state so critical that he is making four stops there in two days this week.

Romney’s advisers acknowledge that he still has work to do in Ohio. Just days ago, Romney moved five campaign workers to that state from Pennsylvania, one aide said. And though the Ohio race has become more competitive — with Romney drawing within five percentage points of President Obama, according to a CNN/ORC International poll released Tuesday — the president still holds a lead in the state, without which no Republican has ever won the presidency.

If the electoral map for Romney remains relatively fixed, the same appears true for Obama, whose advisers say they are committed to the handful of states they targeted months ago. When the president seemed to hold a commanding lead across numerous states early last week, his strategists said they would not make a concerted play for some that appeared almost within reach, such as Arizona. Now that the race is closer, they say they are fortifying their borders, which allow him several options for getting to 270 electoral votes.

Explore the 2012 electoral map and view historical results and demographics

“What you’ve seen is a stable map for a very long time,” Jim Messina, Obama’s campaign manager, said in an interview Tuesday.

The result is the smallest, most rigid playing field in recent history — one that excludes 41 states.

Locked-up states

Both campaigns agree that 36 states are not competitive this year, with 22 of them expected to vote for Romney and 14 for Obama. But the Obama states are more populous; when tallied according to electoral votes, these three dozen states give Obama 197 votes and Romney 169.

Obama and Romney have spent the bulk of their money and attention this year in Colorado, Florida, Iowa, Nevada, New Hampshire, North Carolina, Ohio, Virginia and Wisconsin. Five more states are not being heavily contested, though the campaigns do not agree that the outcomes there are certain.

No state illustrates the narrowness of the playing field more than Ohio, where the candidates are spending more time than anywhere else. Even with Romney’s uptick in national polls, victory remains virtually impossible for him without Ohio; he could win Florida, Virginia, Colorado and Nevada and still lose without the Buckeye State. If anything, his bounce has pushed him to redouble his efforts within the existing electoral map rather than think about expanding it.

For Obama, there is no move to expand the map because he doesn’t need any more states to win. His advisers also say there is no need, at least yet, to rejigger resources because they have been investing heavily all along. Ohio is a case in point: Obama has a paid staff of 700 on the ground there, and his advertising spending, though even with Romney’s now, dwarfed that of his rival for much of the year.

“Ohio is a couple of things: It’s winnable, it’s expensive, and it’s volatile,” said Liz Brown, daughter of Sen. Sherrod Brown (D-Ohio) and the head of the state Democratic Party’s coordinated campaign, a joint get-out-the-vote effort of the party and the candidates. “The last few weeks we’ve gone from ‘Obama’s won Ohio’ to ‘Oh cr--, he gave a less-than-optimistic debate performance.’ This up and down of the narrative around Ohio doesn’t change those three facts. The strategy from the beginning has been a larger investment per capita in Ohio.”

Certainly, Romney could still be tempted to make a more aggressive play for Pennsylvania or Michigan, states that have long been labeled battlegrounds — but that have tilted heavily toward Democrats in recent elections. And Obama, when he held a solid lead in virtually every swing state, was encouraged by some fellow Democrats to extend his ads into Arizona, Missouri and Indiana, three Republican-leaning states.

Romney political director Rich Beeson said he doesn’t rule out an expansion of the map in the campaign’s final month. He cautioned that the movement of staff members from Pennsylvania to Ohio does not signal a concession in Pennsylvania but rather reflects the importance of early voting in Ohio. The staffers will probably return to Pennsylvania before Nov. 6, he said. Beeson also noted that this year, compared with past years, more states are closely contested late in the cycle.

“There are a lot of states out there moving,” he said.

But unlike in some past election cycles — such as in 2000, when George W. Bush swooped into long-shot New Jersey just before ballots were cast — the Obama and Romney campaigns are showing unusual restraint by sticking to their long-standing electoral strategies.

“A lot of it’s just got to do with the polarization of the country,” said Phil Musser, a Republican strategist helping the Romney campaign. “The states that are purple are relatively few in number. The states that are red and blue are relatively large in number. Presidential contests are directly correlated to where you have split population centers that produce mixed results.”

Shrinking the field

A few factors explain why this year’s playing field is so small and unchanging.

First, demographic shifts have taken past battlegrounds off the map. New Mexico, for instance, was in the red column just eight years ago, when Bush won the state and his second term. Since then, both sides have seen it as irreversibly blue.

Similarly, Indiana, which Obama won four years ago, was deemed out of reach for him early on because its conservative electorate does not favor his policies. Even TV ads that have wafted into northeastern Indiana from several Ohio markets haven’t moved the needle. The same is true for northwest Arizona, where households have been inundated with TV ads from Las Vegas stations but polling numbers haven’t changed.

“There’s no evidence of spillover,” said Fred Yang, a Democratic pollster who recently helped conduct the Howey/DePauw poll in Indiana. “Obama is losing by big margins.”

Another factor is the rise in data about where voters are, who they are and whether they can be persuaded to vote a certain way. Through commercial databases, polling, phone-banking and door-knocking, campaigns know more about voters than ever before. They know who is persuadable and who is not. They know how many contacts it takes to reach a voter, how much that would cost and whether that cost is worthwhile, given how liberal or conservative — how winnable — a state is.

Some states move in and out of the competitive zone. At the outset of this election cycle, advisers from both parties thought Arizona, New Mexico, Pennsylvania or Michigan might drift into play. Additionally, outside groups have aired ads in a wider field that has included Pennsylvania, Minnesota and Michigan. But those lists have shrunk recently. A confluence of circumstances — including growing Latino populations and the popularity of Obama’s auto-industry bailout — have given this year’s playing field its uniquely narrow borders.

It’s possible that the field could shrink further, but only if Obama pulls out of states he decides he can’t win or doesn’t need. North Carolina is the best example of this: It has been rated by most pollsters as a likely win for Romney, but the president has invested heavily there, perhaps only to force Romney to do the same. If that was the strategy, it worked; Republicans have spent tens of millions on the airwaves in North Carolina to match Obama’s investment, and Romney is scheduled to travel there for a campaign appearance Thursday.

Romney has few such options. He needs to win more swing states overall, meaning he can’t afford to pull out of any of them without looking like he’s conceding the race.

Dan Keating contributed to this story.