If you're a Republican senator running for reelection this year, the odds you're facing a primary challenger are 50/50. Literally.

Mississippi state Sen. Chris McDaniel (R). (Rogelio V. Solis/AP) Mississippi state Sen. Chris McDaniel (R). (Rogelio V. Solis/AP)

Six of the 12 Republicans seeking another term in November have drawn primary challengers running to their right. But not all campaigns are created equal. While these challengers are often grouped together in conversations about 2014, some stand a much better chance of winning than others.

With that in mind, here's an organized way of thinking about them. We've separated the challengers into three tiers based on their financial muscle, or lack thereof, in light of the latest round of fundraising reports.

The bottom line: Most conservative challengers are not raising much cash.

Tier one (Winning is very possible) 

1. Chris McDaniel: Of all the Republican senators facing primaries, Sen. Thad Cochran (R-Miss.) appears to face the toughest test right now. McDaniel raised $500,000 during his first 10 weeks in the race, more than Cochran raised in the fourth quarter of 2013. Of course, Cochran's got a much bigger war chest, but McDaniel, a state senator, has the support of national tea party groups like the Club for Growth and Senate Conservatives Fund, which should help him close the gap.

Tier two (Maybe, but not likely)

1. Matt Bevin: Bevin, a businessman, brought in a healthy $900,000 during the last three months of 2013, thanks to some help from SCF. In most races, that would be enough to put him in tier one. But this isn't most races. Senate Minority Leader Mitch McConnell (R-Ky.) hauled in $2.2 million during the same period. And have we mentioned on this blog that McConnell's shown a knack for savaging his opponents?

2. Joe Carr: Tennessee Sen. Lamar Alexander's challenger raised $251,000 in the fourth quarter, a better haul than many names on this list. But that was not even half of what Alexander brought in.

3. Milton Wolf: Obama's second cousin, once removed is taking on Sen. Pat Roberts (R-Kan.). But his celebrity status has not caused heaps of cash to flow into his account. Wolf raised $268,000 in the fourth quarter -- not even half of what Roberts pulled in during the same period.

Tier three (Don't hold your breath)

1. Lindsey Graham's opponents: Sen. Graham (R-S.C.) ended the year with $7.6 million in the bank, and his opponents have done nothing to make that figure look any less imposing than it does on first glance. Nancy Mace, the first female graduate of The Citadel, raised just $385,000 last year. Former congressional candidate Richard Cash's fourth quarter haul was unimpressive, and state Sen. Lee Bright acknowledged his fundraising was "struggling." The only thing keeping hope alive for an upset here is South Carolina election law: Graham has to win a majority of the vote to avoid a runoff. If someone can get him in a one-on-one battle, this race would become more interesting.

2. Steve Stockman: Rep. Stockman reported having about $48,000 in the bank at the end of the year (and he was in debt when he launched his surprise 11th hour bid). Sen. John Cornyn (R-Tex.), meanwhile, has a very robust $6.5 million war chest. If you're looking for an upset this cycle, look elsewhere: This race isn't shaping up as fertile ground for one.