(CNN) -- As last night's Republican presidential debate over national security issues demonstrated, credibility is crucial to winning a debate.





Think of credibility like money you have in a bank. Each time you stretch it thin, you have less the next time you might need it. It is your own personal bank of believability.





Knowing your arguments and facts is one way to gain credibility. Mitt Romney fattened his credibility bank account at the expense of Rick Perry, who supported a no fly zone over Syria. Romney argued that a no fly zone over Syria would be pointless since the Syrian government has 5,000 tanks. Romney jokingly said it would make more sense to impose a "no drive zone."





Jon Huntsman made a similar deposit when he stated that sanctions on Iran would not work since "the Chinese aren't going to play ball and the Russians aren't going to play ball," and Iran has already decided to go nuclear. Huntsman's cited the examples of Libya (which gave up its nuclear ambition, and later the government was overthrown with the help of the United States) and North Korea (which has tested nuclear weapons and whose government is still in power.)





Another way to maintain credibility is to cite proof for your arguments. Michele Bachmann has said things in previous debates (President Obama wants Medicare to collapse) and in last night's debate (suggesting that the CIA cannot interrogate terrorist suspects any longer because the ACLU is in charge) that were not very credible. These frequent ATM withdrawals hurt Bachmann because a lack of believability spills over.





Her disagreement with Rick Perry about whether to give aid to Pakistan should have been an excellent point for her. She showcased her knowledge of the subject, saying that we exchange intelligence information and the United States must have our interest represented. Bachmann called Pakistan "too nuclear to fail," and chastised Perry for being naÃ¯ve when he said he would not give Pakistan one penny until it proved it had America's best interests in mind.





This was a terrific answer that warranted applause because it was thoughtful, logical and well reasoned. What did she get? Crickets. Why? Because her believability bank is in the red.





Ron Paul is an enigma. He can provide such thoughtful answers at one time and later interject completely unsubstantiated statements. He was banking responsibly with his argument that the war on drugs was a failure and a reason for much of the violence in Mexico. Paul reminded us that prescription drugs kill many more people than illegal drugs do and that alcohol is a deadly drug.





Paul's argument was factually accurate, even if unpopular with many conservatives. But then Paul writes an overdraft with moderate Republicans by saying things like aid to Africa for malaria or AIDS prevention is "all worthless." Paul hit the daily double. Unpopular answer? Check. Wrong on facts? Check. There are countless examples of disease prevention aid being effective. Could aid be more effective? Sure. But that was not Paul's answer. He simply asserted that aid is worthless, but he had no proof.





Answering questions with non-answers simply isn't credible. For example, Herman Cain twice last night reached into a very old bag of tricks to answer questions with the standard "I'd consult the experts" line.





Actually, he originally answered a question about terrorist profiling with his support of "targeted identification." But when asked a follow-up not 20 seconds later, he retreated by saying he would "ask the professionals."





Nothing hurts your credibility worse than flip-flopping on the same question and diving into a non-answer. Cain's bank account is probably under a thousand dollars. But that still leaves him 999.





Finally, to save credibility, you should be prepared to defend your position when giving a potentially unpopular answer. Newt Gingrich had two answers that the conservative wing of his party might not like, but he defended them well. Gingrich said it was possible to cut some of the military because, "If it takes 15 to 20 years to build a weapons system when Apple changes technology every
who added to their credibility? What was successfully defended
Mitt Romney two answers
question: who added to their credibility?, answer: Mitt Romney | question: What was successfully defended, answer: two answers