A wager, a new nickname and a discussion of “marital infidelity” were among the top topics in tonight’s televised debate among six Republican presidential candidates.

Front-runner Newt Gingrich went into the event vowing to run a “relentlessly positive” campaign and he was tested about 20 minutes after the broadcast started when rival Mitt Romney listed a litany of issue differences.

“But the real difference, I believe, is our backgrounds,” Romney said. “I spent my life in the private sector. I understand how the economy works and I believe that for Americans to say, ‘Good-bye’ to President Obama and elect a Republican, they need to have confidence that the person they’re electing knows how to make this economy work again and create jobs for the American middle class.”

Romney didn’t use the phrase “career politician” to describe the former house speaker, but Gingrich used it in his retort.

“Let’s be candid. The only reason you didn’t become a career politician is you lost to Teddy Kennedy in 1994,” Gingrich said, as the crowd erupted in both boos and applause. “I’m just saying I looked at it and I thought, you know, I’m a citizen. I’ve served the country in many ways. You’re a citizen. You’ve served the country in many ways, but it’s a bit much. You’d have been a 17-year politician by now if you’d won.” 

Romney said losing that U.S. senate race put him back in the private sector.

“We don’t need folks who are lifetime Washington people to get this country out of the mess it’s in,” Romney said. “We need people from outside Washington.”

Ron Paul suggested taxpayers should be “annoyed” that Gingrich had worked for Freddie Mac.

“Now, Freddie Mac is essentially a government organization. While he was earning a lot of money from Freddie Mac, I was fighting for over a decade to try to explain to people where the housing bubble was coming from, (but) Freddie Mac got bailed out,” Paul said. “So, in a way, Newt, I think you probably got some of our taxpayers’ money.”

Gingrich, as he has in the past, stressed that he did not lobby for Freddie Mac, then Michele Bachmann weighed in by criticizing both Gingrich and Romney for their support of a health insurance mandate.

“If you look at ‘Newt Romney’ they were for ObamaCare principles. If you look at ‘Newt Romney’ they were for cap and trade,” Bachmann said. “…If you want a different, Michele Bachman is the proven conservative. It’s not ‘Newt Romney.'”

The topic of marital infidelity was raised by debate moderators Diane Sawyer and George Stephanopoulous of ABC News. Rick Perry was the only candidate to directly suggest Gingrich’s background of two divorces and three marriages might disqualify him for the presidency.

“If you will cheat on your spouse, then why wouldn’t you cheat on your business partner?” Perry asked. “Or why wouldn’t you cheat on anybody, for that matter?” 

Rick Santorum said cheating on a spouse is not necessarily a “disqualifier” for the presidency.

“But certainly it’s a factor and it should be factor,” Santorum said. “You’re electing a leader. You’re electing someone that trust is everything and particularly in this election. In this election, (from) the people of Iowa — I hear this all the time: who can we trust?”

Gingrich said it’s a “real issue” that voters have a right to ask about.

“I’ve said up front, openly, I’ve made mistakes at times. I’ve had to go to God for forgiveness. I’ve had to seek reconciliation, but I’m also a 68-year-old grandfather and I think people have to measure who I am now and whether I’m a person they can trust,” Gingrich said. “And all I can tell you is I’m delighted that people have been willing to look at who I am and what my record has been.” 

Another moment in the debate has captured the attention of throngs of tweeters and bloggers. Perry was pressing Romney on an issue, and Romney offered to make a $10,000 bet on the topic.  Perry said he wasn’t in the “betting business.”

Democrats quickly said the exchange shows Romney is out of touch with the plight of the middle class. A Romney aide said it was the candidate’s “very human” way of trying to get Perry to “shut up.” 

The debate aired nationwide on ABC TV and was co-sponsored by The Des Moines Register and the Republican Party of Iowa.