Voters head to the polls today in six states to cast ballots in a the latest round of primary and runoff elections in the heart of nominating season. The marquee congressional contest is in South Carolina, where there is really only one number on the mind of Sen. Lindsey O. Graham (R): 50 percent.

That's because if Graham can crack the 50 percent mark against six minor primary competitors, he will win his party's nomination outright and advance to the general election without having to endure a top two runoff. (Just ask Sen. Thad Cochran (R-Miss.) how much fun runoffs are.) In a state as ruby red as South Carolina, Graham would be a virtual shoo-in to win a third term in November. That would be a pretty remarkable position to be in for a Republican viewed as a top tea party target at the beginning of this election cycle.

In this Sept. 3, 2013 file photo Sen. Lindsey Graham, R-S.C. talks to a reporter following a speech in Goose Creek, S.C. AP Photo/Bruce Smith

Recent polling has shown Graham hovering right around the 50 percent mark, so he has a pretty good chance of celebrating tonight. Even if he is forced into a runoff, Graham would not be in nearly as much immediate danger as Cochran found himself in last week against tea party challenger Chris McDaniel. Well-funded national tea party groups lined up behind McDaniel from the day he launched his campaign. In South Carolina, Graham's challengers simply don't have that kind of support.

The competition (or lack thereof) is a big reason why Graham — who is viewed with skepticism on the right over his embrace of immigration reform, among other things — is not seriously imperiled. His challengers are Bill Connor, Benjamin Dunn, Richard Cash, Det Bowers, Nancy Mace and Lee Bright.

Who? Exactly.

Politico reported earlier this year that Graham deployed the honey > vinegar approach when it came to potential big-name challengers like Rep. Mick Mulvaney, reaching out them early and helping with whatever they needed. The more than $6.4 million Graham raised since the start of 2013 gave his would-be competition even more justification not to challenge him.

The lesson to take away from Graham, should he win today, is that 1) Preparing very, very early is the best way to beat back tea party dissatisfaction and 2) You are only as vulnerable as the challenger(s) you face are strong. If you can keep top or even medium tier opponents away from you, you're going to stand a good chance of winning no matter how much unhappiness there is with your record.

Here are the four other biggest things to watch today:

1. Will Don Beyer seal the deal in Virginia's 8th district?

The race to replace long-serving Rep. James P. Moran (D) in a Northern Virginia congressional district will essentially be over after today. That's because the winner of the Democratic nomination will be on cruise control headed toward November since the district is one of the most liberal in the country. The Democratic frontrunner is Don Beyer, who served as lieutenant governor in the 1990s and bundled contributions for President Obama's 2008 campaign before being rewarded with a plum ambassadorship. Beyer faces six other Democrats who don't have the money nor the name recognition (he co-owns area car dealerships bearing his name) to match him. There has been little policy daylight between the contenders in this race; in such a contest the candidate with the most robust campaign operation is usually the one who wins. This race is shaping up as no exception.

2. Eric Cantor will probably win his primary. But by how much?

Polls show House Majority Leader Eric Cantor (R-Va.) leading his primary opponent by between 11 and 34 point heading into today. In other words, he's almost certainly going to win. But his margin over tea party challenger David Brat, who he has not taken lightly, will still be closely watched. A 20-point victory would likely quiet the murmurs about tea party frustration with Cantor back home. A 10-point win may only stoke them.

3. The Republican primary for lieutenant governor in Nevada is the under-the-radar race to know. 

For more on why the Nevada lieutenant governor's race is the most important contest you've never heard of, read this. The short version: If a Democrat wins the LG seat in this year's open race, it could give Gov. Brian Sandoval (R) pause about challenging Senate Majority Leader Harry M. Reid (D-Nev.) in 2016 since Sandoval would be replaced by a Democrat, mid-term. That's why Reid's counting on Assemblywoman Lucy Flores (D), a capable up-and-comer, in the fall. But who will Flores, favored to win the Democratic nomination, face in November? The depends on today;'s GOP primary. Sandoval and the GOP establishment like state Sen. Mark Hutchison. But former state Sen. Sue Lowden is running as the more conservative candidate. Yes, that's the same Lowden who ran for Reid's Senate seat in 2010. If she wins the primary, Flores could have an easier path to victory in the fall.

4. Maine's 2nd congressional district primary will whittle the field in a competitive seat. 

Rep. Mike Michaud (D) is running for governor, leaving behind a competitive district where Obama won 53 percent of the vote in 2012. State Sen. Emily Cain (D) was featured in The Fix's 40 Under 40 list of rising stars. She faces fellow state Sen. Troy Jackson (D), who sounds less willing to compromise with the other side, in the primary. The Republican race is between former state treasurer and gubernatorial candidate Bruce Poliquin, and Kevin Raye, who lost to Michaud in 2002 and 2012.