Democrats have been saying for a long time that the House could be in play in 2012, and now some Republicans are starting to join them.

“For Democrats to take 25 seats, they will need a wave,” former congressman Tom Davis wrote in an op-ed in The Hill recently. “Continued polarization and obstruction could create such a wave.”

Former Republican National Committee chairman Michael Steele agreed that keeping the majority isn’t a done deal: “It could be very, very hard.”

And last week, a member of the conservative Wall Street Journal editorial board opined that the GOP majority could be in jeopardy if Republicans don’t make it a priority.

“The House is no sure thing,” wrote Kimberly A. Strassel.

In fact, there is a growing behind-the-scenes sense among House Republican leaders that the more the presidential race has enveloped the daily news, the importance of keeping the House has been lost – exactly the point Strassel sought to make.

Combine that with some recent momentum for Democrats, and it’s causing some unease.

These three opinions, it should be noted, do not represent any kind of consensus within the Republican Party. Publicly, GOP leaders have been bullish on their prospects.

“I just don’t think there’s a possibility that it happens,” said former congressman Tom Reynolds (R-N.Y.), who, like Davis, is a former chairman of the National Republican Congressional Committee. “With a 25-seat majority, I just don’t think they can get that much.”

House Speaker John Boehner of Ohio speaks during a news conference on Capitol Hill last week. (Luis M. Alvarez/Associated Press)

Given that we’ve seen three straight election cycles with at least 24 seats changing parties, is it really that outlandish to think a 25-seat GOP majority isn’t safe?

Of course not. In today’s electoral environment, there are few majorities that are safe. And Republicans may well find themselves fighting to hold the House this year.

But that doesn’t mean it’s likely or even probable.

Below, we explore some of the reasons why it’s possible and why it’s unlikely.

Why it’s possible:

1. The generic ballot: Democrats have been hyping this measure for a long time. It basically shows that, given a choice between a nameless, faceless Republican and a nameless, faceless Democrat, voters right now prefer the Democrat – and by several points in some polls.

Republicans, though, note that Democrats generally have a small advantage on this measure. “They’ve done a heckuva spin” on the generic ballot, Reynolds said. “I think the generic ballot’s something to watch, but when I was chair, if Democrats had a four-point advantage, I looked at that as even.”

2. Obama’s momentum: Don’t look now, but the country just had two good jobs reports in a row, and President Obama’s personal approval rating rose to 50 percent in a new Washington Post-ABC News poll.

On some level, the House election is really an extension of the presidential race, and for Democrats to retake the House, they probably have to keep the White House. That looks like more of a possibility today than it did Jan. 1.

3. Fundraising: While the GOP has a House majority, the Democratic Congressional Campaign Committee actually outraised the NRCC by about $7 million dollars in 2011. On top of that, Democratic challengers outraised more than a dozen GOP incumbents in the fourth quarter of 2011 – a strong sign of the quality of Democratic candidates.

You need candidates and money to win a majority, and Democrats appear to be checking both of those boxes.

4. History: Republicans have held this many seats five times since 1900, and each time they sustained huge losses in the next election – an average loss of 48 seats.

Of course, this all happened more than 60 years ago, when bigger swings were much more commonplace. Republicans haven’t had a majority this big since the 1940s, so there’s no recent apples-to-apples comparison.

Why it’s unlikely:

1. Democratic retirements: House Democrats have been bitten more by the retirement bug than Republicans. The minority party, as it often does after losing its majority, has lost more members overall — 20 Democrats are either retiring or running for higher office, compared to 14 Republicans — and their retirees come from tougher districts, too.

According to the Cook Political Report, Republicans are favored to win five districts held by retiring Democrats, and Democrats aren’t favored to win any seats held by retiring Republicans. In other words, if the GOP can win these seats, Democrats will actually have to win 30 seats to retake the majority.

2. Super PACs: Whatever advantage the DCCC has over the NRCC is likely to be wiped out — and then some — by Republican-leaning super PACs who should plug tens of millions of dollars into keeping the House.

Even if GOP leaders may not be as focused on the House as some would like, American Crossroads is essentially a second NRCC ready to put its money on the table to save the majority, and there’s really no comparable Democratic equivalent. This matters big time.

3. Redistricting: While maybe not as big a windfall for the GOP as it had hoped, redistricting has helped Republicans shore up some of their most vulnerable members. In most cases, these members got a few points better and will still have to defend themselves, but overall it’s a boon to the GOP.

4. History: For every historical justification, there’s an inverse. History shows it’s exceedingly rare for the president’s party to win control of the House when that president is up for reelection. More often than not, the president’s party makes modest gains, if at all.

Even when Ronald Reagan won a resounding reelection victory in 1984, his party gained just 16 seats. In fact, the last time a president’s party has won more than 25 seats while the president was being reelected was 1964.