Rep. Vance McAllister, R-La., projected a family man persona to win an election. But his idealized campaign ads clearly didn't show the whole picture.

Just 20 days after publicly boasting about his "good guy" reputation, McAllister was caught on a surveillance camera kissing a married female staffer, video that came to light on Monday.

"If I had a dollar for every time that I've been told, 'You're a good guy, but don't let them change you, don't become one of them,' I probably would have been able to self-fund my campaign a lot easier," a newly elected McAllister told ABC's Jeff Zeleny in a Dec. 3 interview.

Then, on Dec. 23, the "family man" was filmed kissing a married staffer in his district office.

Few people knew of the affair until an anonymous source tipped off McAllister's hometown newspaper, The Ouachita Citizen , this week. As media coverage snowballed, McAllister issued a public apology.

"There's no doubt I've fallen short …. I'm asking for forgiveness from God, my wife, my kids, my staff, and my constituents who elected me to serve," he said.

The conservative Christian congressman - married with five children - ran on a platform of "faith, family, and country" and relied on his unsullied image to attract voters.

In one campaign ad, McAllister claimed he was running for office because "Louisiana values … are sorely missed in Washington, DC."

Even after he was elected, McAllister continued to promote the family man persona, insisting that he wouldn't let his congressional responsibilities keep him from cooking Sunday breakfast for his family.

When Zeleny suggested his culinary expertise might make him very popular in Washington, the congressman responded, "We're up here to go to work, not to … socialize … but it seems like there's a lot of that that goes on."

McAllister aides confirmed to the Washington Post that the staffer in question, Melissa Anne Hixon Peacock, 33, is no longer on the congressman's payroll. They also say the congressman's wife knew about the affair before the video became public and that McAllister does not intend to resign.

ABC News' Jeff Zeleny contributed to this report.