Attacked as a lifelong Washington insider, newly minted Republican front-runner Newt Gingrich parried criticism from Mitt Romney in a campaign debate Saturday night in Des Moines, telling the former Massachusetts governor, “The only reason you didn’t become a career politician is because you lost to Teddy Kennedy in 1994.”

Gingrich also defended himself against attacks from Texas Rep. Ron Paul and Minnesota Rep. Michele Bachmann in the first debate since he soared to the lead in polls nationally and in Iowa. The state’s caucuses on Jan. 3 will kick off the competition for Republican National Convention delegates who will pick an opponent to President Barack Obama.

All six Republicans on stage assailed Obama’s handling of the economy, the overriding issue of the election, yet split down the middle on legislation making its way toward a year-end vote in Congress to extend a Social Security payroll tax cut into 2012.

Romney, Gingrich and Paul said they favored it. Bachmann, Texas Gov., Rick Perry and former Pennsylvania Sen. Rick Santorum opposed the measure.

The internal disagreement could well portend difficulties for legislation that Obama has proposed and Republican leaders in Congress view as essential if the party is to avoid being tagged for raising taxes.

Gingrich’s personal life has become a campaign issue, too, and it came up briefly Saturday night.

Gingrich, who has been divorced twice and has admitted past infidelity, said the issue was an important one, then added, “I’ve made mistakes at times and I’ve had to go to God for forgiveness.”