Good Saturday morning, and happy caucus and primary day. Polls are already open in South Carolina, where they close at 7 p.m. Eastern. Nevada Republicans head to their caucuses at noon., with results coming in by 1:30 p.m., while the Democrats start at 2:00 p.m. and hope to be done in an hour or two. Results are expected by 5:00 p.m. Eastern. Meanwhile, here's what Washington is watching today:

-- With poll numbers getting out of hand in South Carolina, Nevada is becoming more important for Hillary Clinton than Barack Obama. She needs a win here today, and she is in good position to get it: Clinton leads the latest RCP Nevada Average by four points. Previous contests this year have not given the winner a big boost, meaning that Clinton can't expect a Nevada victory to help close the gap down south, where Obama leads the latest RCP South Carolina Average by 9.6 points. Clinton, though, needs to sustain some momentum going in to February 5. Having lost three of the first four meaningful contests is not the way to build the big mo'.

-- Clinton campaign strategist Mark Penn sounds awfully coy when "downplaying" -- and we use quotation marks for a reason -- expectations in Nevada in a memo out yesterday. Citing an Obama campaign official who said the candidate who wins the Culinary Workers' endorsement is most likely to win the caucuses, Penn says the nine Strip-based caucus sites will play a huge role in the process, and that the Obama campaign begins the day with a 5-point advantage. "If the polls turnout differently from the result, there may be an easy explanation for it this time," he concludes, blaming any loss Clinton might suffer on the special caucus sites.

-- Meanwhile, we suggested yesterday that perhaps Nevada was a state Edwards should have focused on more. He may begin to realize that he won't win the nomination, but he's still accumulating a good number of delegates. By the end of the contest, John Edwards could be the kingmaker who decides which Democrat wins the nomination, Ben Smith suggests. An underlying, and surprising, point that reveals itself: Like Romney, leading Democrats are planning for a long fight as well.

-- Fred Thompson has the most on the line today for Republicans. He has essentially staked his entire campaign on South Carolina. If he falls flat, he will become the first major Republican candidate to get out of the way. If he comes in a close second or third, with candidates bunched together, he might decide to stay in. After losing Michigan, Mike Huckabee and John McCain could each do with a victory too; McCain leads the latest RCP South Carolina Average by just one point, though that margin is falling as Huckabee closes the gap. Each could use the momentum heading into Florida and February 5. No one, though, is in more need of something that looks like a win than Thompson.

-- There isn't a cloud in the sky over Las Vegas. There is, however, significant cloud cover around South Carolina. The National Weather Service has issued a snow advisory for the Greenville-Spartanburg area, as Jonathan Martin points out, where Mike Huckabee and Fred Thompson are said to have strong bases; 1-3 inches are expected. Columbia is under a winter weather warning, while rain will fall throughout the day closer to the coasts. The effect the weather will have on turnout could be the difference between a nail-biter and a blowout tonight.

-- After today, Democrats turn their attention to South Carolina and beyond. On their way to the Palmetto State, each candidate is making stops around the country in key February 5 states as they begin the delicate process of deciding how to approach Super Duper Tuesday. Is it more cost effective to buy ads in each of the twenty-two states that will vote that day, or should the candidates purchase spots on national television? AdAge reports media buyers from the Clinton and Obama camps have each contacted at least one network about national air time.

-- Republicans, meanwhile, turn their attention to Florida, and everyone gets their first taste of Rudy Giuliani in several weeks. Giuliani's poll numbers have slipped in recent weeks -- he now trails McCain by 2.9 points in the latest RCP Florida Average -- but because of a long tour of the state and a constant television presence, which other candidates lack, it's not smart to write him off just yet.

-- On the other hand, what if McCain picks up a major endorsement before the January 29 primary? It seems that Senator and former RNC chairman Mel Martinez is on McCain's Monday schedule, and a nod of support is rumored, the Miami Herald blogs. Rumor has it, as well, that Governor Charlie Crist has been asking around on whether he should back McCain, who came out early for the then-Attorney General's bid for the state's top job. Either, or both, endorsements could seal Florida for McCain.

-- Worst GOTV Ad Ever: Usually, our bit is something "of the day." But this deserves an "ever": Pizza Hut, trying to be hip and with it, is urging their customers to get out and vote in a new television spot. And apparently, their pizza-munching protagonist doesn't believe in this whole "change" thing, yet still easily convinces his pizza-stealing buddy to go vote. Truly, never has a worse campaign ad been made. The ads are running in Nevada and South Carolina.

-- Today On The Trail: John McCain visits a polling place in Charleston before holding his victory party there. Mike Huckabee's victory party is in Columbia, as is Fred Thompson's, their only public events of the day. Mitt Romney rallies with voters in Jacksonville, while Rudy Giuliani will meet older voters at The Villages, both in Florida. Ron Paul hits precincts in Charleston, Lexington and Columbia before rallying with supporters there. On the Democratic side, Hillary Clinton visits with Las Vegas supporters as caucus results roll in. Later she attends an event with voters in St. Louis. John Edwards rallies with voters in Atlanta before hopping over to Greenville, South Carolina. Obama is down today, but picks up tomorrow with stops in Atlanta and Columbia.