GOP presidential candidate Herman Cain (Getty Images)

CNN analyst Roland S. Martin writes in a blog entry that as GOP presidential candidate Herman Cain continues to rise in popularity among conservatives, he needs to sharpen his knowledge of certain issues, especially foreign policy, so that a broader swath of voters will take him seriously. 

Former Godfather's Pizza CEO Herman Cain has vaulted to the top of the Republican presidential field because GOP voters like his plainspoken talk and his willingness to offer a radical change to the U.S. tax code, and in a year when touting a long career in politics isn't a good idea, he's getting points for having no political experience.

But just as it is easy to vault up the ladder, it is just as easy to come falling back down when people really begin to start taking everything you say seriously, which should always be the case when running for president of the United States.

It was clear at CNN's Republican debate Tuesday in Las Vegas that the other six candidates on stage weren't going to let Cain skate through another debate touting his "9-9-9" tax plan and smiling and joking. The knives came out quickly, and the former conservative radio show host must have felt like he was ambushed. 

Read Roland S. Martin's entire blog entry at CNN.