Elections are all about turnout.

That may be the biggest no-brainer in campaign reporting. After all, whichever side gets more votes, um, wins. (In sports, the team with the higher score is more likely to emerge victorious, too.)

Turnout is predicated on excitement. Voters who feel passionate about an election are far more likely to vote. And if one party’s voters are eager to turn out while the other side’s aren’t, it almost always produces major political upheaval.

If new numbers from Gallup are to be believed, this “intensity gap” is a major problem for President Obama as he looks toward 2012.

The data showed that just 45 percent of Democrats say they are more enthusiastic about the 2012 presidential election than they have been in past elections, while 44 percent described themselves as less enthusiastic.

Nearly six in 10 Republicans (58 percent), on the other hand, call themselves more enthusiastic about voting in 2012 than in past contests, while just 30 percent say they are less excited.

The disparity between Democratic and Republican enthusiasm is the largest measured by Gallup since 2000 and is a major departure from the months leading up to the 2008 presidential election, when Democrats held an intensity advantage of 40 points or more.

The current intensity gap is having real-world effects. Two special elections — one in New York City, the other in (mostly) rural Nevada — held in mid-September went for Republicans. While the Nevada seat was in a GOP-leaning district, the Brooklyn and Queens seat hadn’t been held by a Republican for more than eight decades. The defeated Democrat, David Weprin, told the New York Post that “the message of the campaign was ‘Send Obama a message.’ ”

Steven Law, the head of American Crossroads, a large, conservative-aligned outside interest group, said, “The intensity surge on our side is new since the spring and almost 100 percent focused on Obama.”

Some of the difference in excitement levels between the parties is to be expected. The party not in power (or at least not in the White House) tends to be more energized as it seeks to win it back than does the side in control. In 2008, for example, 79 percent of Democrats said they were more enthusiastic about voting than they were in past elections — ready to send a message after eight years of the George W. Bush presidency.

But whether it’s par for the course or not, it remains an issue for Democrats up and down the ballot.

Hoping to close the intensity gap, Obama has begun to focus far more heavily on his party base while on the stump — seeking to set the stakes of the election by noting what Republicans would do if they won the White House.

“I have to make sure that our side is as passionate and as motivated and is working just as hard as the folks on the other side, because this is a contest of values,” Obama said at a fundraiser in San Jose last week. On that same West Coast trip, he urged attendees at a Seattle event to “shake off any doldrums.”

The ramping-up of Obama’s rhetoric is being echoed at the organizational level as the president’s political machine — built in 2008 and maintained since then for this moment — has increased its efforts to engage the twin pillars of the president’s base: minorities and young people.

Ben LaBolt, a spokesman for the Obama campaign, said it’s “logical” that Republicans would have an intensity edge, because they are “fully engaged in a primary contest right now.”

But, he added, when “Democrats face the choice next year between a president who is fighting every day to provide economic security for the middle class and a Republican nominee that wants to go back to cutting taxes for millionaires and billionaires, maintaining tax breaks for large corporations and allowing Wall Street to write its own rules, there’s no doubt that the president’s supporters will be mobilized in force.”

Doubts remain, however, about the president’s ability to rev up a base. He’s had a testy relationship with core voters at times because of the belief that he has been insufficiently loyal to the cause.

Even Obama’s closest allies acknowledge that the excitement that grew organically around his candidacy in 2008 will be difficult to replicate after four years of incumbency and a still-struggling economy.

“It’s getting late in the game to solve it any other way than making a huge contrast with what we hope will be a more flawed GOP nominee,” said Paul Maslin, a Democratic pollster. “One more Obama speech sure won’t change anything.”