"This could be heaven or this could be hell," sang the Eagles in "Hotel California," and there may be no more apt summary of what's at stake for the four remaining major presidential candidates in Tuesday's contest in the Golden State. With polls showing a close race on both sides, victory in California for putative underdogs Barack Obama and Mitt Romney could catapult them to frontrunner status--while a bigger-than-expected loss could doom their chances. In a mammoth state where New Hampshire-style retail politics will get you nowhere, momentum, endorsements, and media coverage (both paid and free) should make the difference.

Delegates: For the Democrats, 370 of the state's 441 delegates are at stake on Tuesday (the rest are superdelegates). 241 delegates will be awarded proportionally based on the results in the state's 53 congressional districts; 129 will be awarded proportionally based on the statewide results. For the Republicans, 170 of the state's 173 delegates are at stake. (The three additional delegates are state and national party representatives.) In each of the state's 53 congressional districts, the candidate receiving a plurality of the vote will receive three delegates, for a total of 159 delegates awarded at the district level. A further 11 delegates will be awarded to the winner of the statewide vote.

Format: The Democratic primary is open to registered Democrats and independents; the Republican primary is closed to independents. This promises to give a boost to Obama (in the latest Field Poll, he beat Hillary Clinton among independents 54-32), but it's unclear how many independents will show up (especially if Clinton keeps push-polling them). Romney also stands to benefit, since John McCain won't be able to draw on the independent support that has bolstered him in past states.

Polls: On the Democratic side, the average of the latest polls finds a statistical dead heat, with Clinton holding a lead of 0.2 percent. The latest Reuters/Zogby poll, released on Monday, finds a six-point Obama lead, though Mason-Dixon has her up nine. The widely respected Field Poll has Clinton up two, with a quarter of voters still undecided. This is a remarkable turnaround from just a week or two earlier, when she held a comfortable double-digit lead. The Republican race is nearly as tight: McCain's average lead is just two points. The polls are all over the map: Zogby has Romney up eight, while Field has McCain up eight and Mason-Dixon has him up nine. The GOP race has been extremely volatile, with Giuliani, McCain, Romney, and Huckabee all having held the lead in various polls over the past six months.

Fundraising and Advertising: California has traditionally been little more than a cash cow for presidential candidates; this year it's a cash cow with a voice. Clinton leads all candidates, having raised $17.2 million in the state; Obama is a close second with $15.1 million. On the Republican side, Romney has hauled in $7.8 million in the state, while McCain trails at $4.4 million.

Advertising statewide in California is prohibitively expensive, and with 20-plus other states voting on Super Tuesday, no candidate can afford a full ad buy. Still, three of the candidates--Clinton, Obama, and Romney--have apparently spent between $1 and $2 million each on network advertising in the state; McCain has spent far less, and is relying primarily on free media and a national cable ad buy.

Endorsements: Back to "Hotel California": "She got a lot of pretty, pretty boys that she calls friends." The Eagles, as always, are right--the three prettiest boys of the California Democratic establishment, San Francisco Mayor Gavin Newsom, Los Angeles Mayor Antonio Villaraigosa, and Assembly Speaker Fabian Núñez, are all backing Clinton. She also boasts the endorsement of the state's most popular Democrat, Senator Dianne Feinstein, and 16 of the state's 34 Democrats in the U.S. House of Representatives. (California's other Democratic senator, Barbara Boxer, has announced her neutrality.)

Obama has cobbled together his own coalition of endorsements, starting with the state's newspapers: The Los Angeles Times, San Francisco Chronicle, San Jose Mercury News, Sacramento Bee, and influential Spanish-language daily La Opinion have all endorsed him. He has also earned the support of 7 of the state's House Democrats, including the influential Education and Labor Committee chairman George Miller, a top lieutenant to Pelosi, whose endorsement has been taken by some as a sign of her tacit support of Obama. After John Edwards dropped out, Obama also won the support of the state's Service Employees International Union. Edwards supporters seem to be moving more heavily toward Obama. And even First Lady Maria Shriver has signed on.

In short, the state is divided. In Hollywood, Steven Spielberg is with Hillary; David Geffen and Jeffrey Katzenberg are with Obama. Representative Loretta Sanchez supports Hillary; her sister, Representative Linda Sanchez, backs Obama. It all adds up to a very, very close election.

On the Republican side, the 800 (okay, 250) pound gorilla, Governor Arnold Schwarzenegger, has endorsed McCain. Schwarzenegger remains popular among rank-and-file Republican voters, but is distrusted by conservative activists, so it's unclear what impact the endorsement will have. Romney is the favorite of the state's conservative Republican congressional delegation: five representatives, including Orange County Representative Dana Rohrabacher, support Romney, while only one, former gubernatorial candidate Dan Lungren, supports McCain.

Demographics: On the Democratic side, the big question is what percentage of the electorate will be Latino. More than a third of the state's residents are, and most Latinos lean Democratic, but in 2004 they made up only 16 percent of the primary electorate. That number will likely go up slightly this time, but so will the black vote, which made up 8 percent of the electorate last time and backs Obama strongly. (Some of the polls showing large Hillary leads estimated the Latino share of the vote at nearly 30 percent, which is almost certainly too high.) California's white Democratic electorate will tip the election one way or the other; it is wealthier, better educated, and more socially liberal than white Democrats in other states are. There's also a geographic divide in the state: Expect Obama to do well in the Bay Area, where there are large numbers of African-Americans and upscale white liberals, and the state's conservative rural areas. Hillary should do better in Los Angeles and the Inland Empire, which has been hit by a wave of home foreclosures and where blue-collar Democrats predominate. It's less clear who will prevail in San Diego County and the Central Valley, the state's traditional general-election battlegrounds.

California may be a blue state overall, but its Republicans are deeply conservative: 61 percent of primary voters in 2000 identified themselves as such. Romney should benefit from the upscale bent of the state's Republicans: in 2000, 43 percent of primary voters made more than $75,000 per year. Latinos in 2000 made up only 8 percent of Republican primary voters. Since then, their share of the population has grown, but their opinion of Republicans has fallen. McCain, endorsed by La Opinion, should get the lion's share of their support, but it's unclear how many votes that translates to. There are more Mormons in California than in any state but Utah, and they could account for 5-10 percent of Republican primary voters--advantage, Romney. The state's huge Asian-American population leans increasingly Democratic, but the Republicans among them tend to be hard-liners on foreign policy from China, Vietnam, and Korea. Expect them to back McCain.

Analysis: There are two key questions on each side. For the Democrats, first, how big is Clinton's lead going into Election Day? A third or more of voters are expected to cast their ballots by mail, and have been voting since early January. Clinton is expected to win among this group, but needs a sizable lead in order to feel comfortable going into Election Day as Obama surges. Second, will independents turn out? Obama's been able to generate enough enthusiasm in other states to drive them to the polls--he needs an enormous turnout among independents, who can only vote in the Democratic primary, to put him over the top.

The Republican contest is increasingly shaping up as one of money (Romney) versus momentum (McCain). Conventional wisdom holds that the former matters more in California politics, but McCain may have garnered enough free media, particularly with the Schwarzenegger endorsement, to pull out a win. The second question is what share of the vote Huckabee will get. It's hard to envision McCain pulling down more than 50 percent of the vote in California, but if committed social conservatives decide they like Mike, that could be it for Mitt.

Finally, keep a close eye on the district-by-district results. On the Democratic side, the competition will be fiercest in congressional districts with an odd number of delegates, where even a narrow victory will translate into an extra delegate. On the Republican side, bizarrely, Nancy Pelosi's 80-percent-Democratic San Francisco district selects just as many delegates as Duncan Hunter's 70-percent-Republican suburban San Diego district. There are more of the former in California than the latter, so whichever candidate does well in Democratic areas (most likely McCain) could win the delegate count even while losing the statewide vote.

For More Information: The Los Angeles Times and San Francisco Chronicle both have politics blogs worth checking out, though with less of a local focus than one might expect. For a more local flavor, check out left-leaning blogs Calitics and the California Progress Report, as well as the right-leaning California Conservative.

Get a rundown of other states at play at TNR's Super Tuesday Primer, updated with new states every day leading up to February 5.