CNN debate moderator John King put all the GOP presidential candidates on the spot about their tax returns Thursday night, asking whether they will make their filings public.

It was an easy question for former House Speaker Newt Gingrich, who released his returns just as the debate began.

Rep. Ron Paul (R-Texas) said he hadn't given the issue much thought and didn't have any intention of doing so.

"I'd probably be embarrassed to put my financial statement up against their income," Paul said, referring to the wealth of the other candidates. "I don't want to be embarrassed because I don't have a greater income. Now, I mean, it may come to that. But right now, I have no intention of doing that."

He added that he has no conflicts of interest, doesn't talk to lobbyists and doesn't "take that kind of money."

Romney, who has faced the most pressure on this topic, said he will release his tax returns in April, if he's the nominee, and would "probably" release his returns from other years as well.

He quickly tried to change the topic, saying Democrats simply wanted to attack people for "being successful."

"And I have been successful," he added before hitting President Obama for playing "90 rounds of golf" while Americans are struggling in the tough economy.

King pointed out that Republicans are often calling on Romney to release his tax filings.

"Why not, should the people of South Carolina, before this election, see last year's return?" asked King to applause from the audience.

"Because I want to make sure that I beat President Obama," replied Romney. "Every time we release things drip by drip, the Democrats go out with another array of attacks. As has been done in the past, I'll put these out at one time so we have one discussion of all of this. I obviously pay all full taxes. I'm honest in my dealings with people. People understand that. My taxes are carefully managed. I pay a lot of taxes. I've been very successful. When I have our taxes ready for this year, I'll release them."

Romney recently revealed that his effective tax rate is 15 percent, below the rate paid by many middle-class families.

Gingrich did not directly attack Romney, saying, "Look, he's got to decide. The people of South Carolina have to decide. If there's anything in there that will help us lose the election, we should know it before the nomination."

Santorum said he does his own taxes.

"They're on my computer and I'm not home," he said. "And there's nobody at home right now until I get home. When I get home, you'll get my taxes."

Finally, Romney refused to commit to the transparency and disclosure of his father, George Romney, who was governor of Michigan. In 1967, the elder Romney released his tax returns for 12 years.

"Maybe. I don't know how many years I'll release," responded Mitt Romney when asked if he'd follow in his father's footsteps. "I'll take a look at what our documents are." The audience booed him.

"I'm not going to apologize for being successful," he added. "I'm not suggesting these people are doing that. But I know the Democrats will go after me on that basis. That's why I want to release these things all at the same time. My dad, as you know, born in Mexico, poor, didn't get a college degree, became head of a car company. I could have stayed in Detroit like him and gotten pulled up in the car -- I went off on my own. I didn't inherit money from my parents. What I have, I earned. I worked hard. The American way."