We'll have full coverage of results tonight right here on Post Politics. In the meantime here are the five biggest story lines to watch today.
1. Who will win the Cochran-McDaniel runoff?
This is the biggest contest of the day, hands down. After one of the nastiest, most divisive and personal campaigns in recent memory, Mississippi voters will decide their Republican nominee for U.S. Senate in a one-on-one runoff. Polls show tea party-backed state Sen. Chris McDaniel with a slight lead, but runoffs are hard to read and so the only thing we know is it looks competitive. McDaniel has a number of things working in his favor: He was the lead vote-getter in the primary; runoffs have tended to favor the challenger in recent years; and the election comes two weeks after a tea party underdog upset Rep. Eric Cantor (R-Va.), capturing national attention. The big questions are whether Sen. Thad Cochran's efforts to return to his roots during the runoff -- reminding voters of all he's done for the state -- and strategy of pursuing black voters will be enough to overcome McDaniel's expected advantages. If McDaniel wins, get to know the name Travis Childers. He's the Democratic nominee and a conservative former congressman Democrats think can make things interesting against the unpredictable McDaniel, even in this deeply red state. If Cochran wins, it's probably game over for Childers.
2. Will we see a runoff in Oklahoma?
As we wrote Monday, the Sooner State race doesn't neatly fit the tea party vs. establishment box, but figures like Sen. Ted Cruz (R-Tex.) and the Senate Conservatives Fund have a lot at stake. They are squarely behind former state House Speaker T.W. Shannon, an African American and Native American rising star running to the right of Rep. James Lankford. Shannon's no outsider, having spent years working in politics. And Lankford is a member of House leadership, but he's not your typical establishmentarian. A little-known Baptist minister in 2010, he came from nowhere to win his congressional seat in an upset, thanks in large part to a loyal base of Christian conservative supporters. The big question is whether anyone gets a majority or whether Lankford and Shannon will be forced into a runoff. There are five other candidates in the mix, including Randy Brogdon, a former gubernatorial candidate with a small but loyal following that could be enough to force a runoff. Observers say Lankford had the momentum during the final week.
3. Will Charlie Rangel survive?
Longtime Rep. Charlie Rangel (D-N.Y.) defeated state Sen. Adriano Espaillat (D) by just 1,000 votes in 2012. He faces another tough race this time around. But polls show Rangel leading. If the Democrat can pull out another win, he is likely to become the second-longest currently serving House member . If he loses, the chatter about whether he stuck around too long and was done in by shifting demographics will be widespread. The 13th District is 52 percent Hispanic.
4. Is another Cantor-style upset in the offing?
Cantor faced a perfect storm in his district. It's hard to say whether that will happen again. But keep an eye on Rep. Richard Hanna (R-N.Y.), who has publicly clashed with the tea party. He faces a primary challenge from Assemblywoman Claudia Tenney (R), who, like Cantor foil Dave Brat, is endorsed by conservative commentator Laura Ingraham. The polling firm Hanna is using is the same one that was used by Cantor. Rick Santorum (R) did robocalls for Tenney that hit thousands of houses Monday.
5. Don't forget the governor's races in Maryland and Colorado.
In Colorado, Gov. John Hickenlooper (D) will learn who his Republican opponent will be in the fall. Secretary of State Scott Gessler and former congressmen Tom Tancredo and Bob Beauprez are vying for the GOP nomination. The GOP establishment is more comfortable with Beauprez than with Tancredo, who has a knack for stoking controversy. Meanwhile, in Maryland Lt. Gov. Anthony Brown is the clear frontrunner for the Democratic nomination. Brown had a 23-point lead over Attorney General Doug Gansler in a recent Washington Post poll. If Brown wins, he would be well on his way to becoming just the third elected black governor in U.S. history.