Rick Santorum joined a bipartisan chorus this January in criticizing fellow Republican presidential candidate Mitt Romney for not releasing his tax returns, but 12 years earlier the former Pennsylvania senator faced similar criticism for refusing to disclose who paid for a family trip to Rome.

In 1999 a Virginia-based nonprofit called the Common Good Foundation paid for Santorum and his wife, Karen, to spend six days in Rome, according to an article in The Philadelphia Inquirier on June 23, 2000.

Santorum followed Senate protocol and filed paperwork showing that the organization, whose website says it is "a movement of faithful Christians dedicated to building a culture of life, family, freedom and solidarity," had paid for his trip.

The controversy started because Congress' rules also require its members to disclose if a donor also pays for his or her family to take a vacation.

Initially, Santorum didn't disclose who paid for his wife and children to make the trip across the Atlantic with him.

Santorum defended witholding the information, saying that because of an exception to the disclosure rule, a spouse who travels for his or her own reasons doesn't need to disclose who footed the bill.

Santorum's spokesman at the time, Robert Traynham, told the Inquirer that the senator's wife traveled to Rome to promote her book Letters to Gabriel.

"Mrs. Santorum is an accomplished author in her own right and was invited under her own merits and based on her credentials," Traynham said. "The children were traveling under her invitation."

The Center for Public Integrity continued to pressure Santorum.

"We need to know the relationships between him and the people who are paying for it," said its managing director Peter Eisner at the time. "Making a legalistic argument that there are exemptions and other such things, and making partial disclosures gives the appearance of trying to hide something."

The senator's campaign eventually revealed that the Common Good Foundation had paid for Mrs. Santorum's trip. It released a statement from the foundation's founder, Keith A. Fournier, to Karen Santorum asserting that "your recent book and long labor in the pro-family movement is a vital part of our decision to sponsor your trip."

Who paid for the children's trips still remains a mystery. Their expenses were underwritten by "private individuals" whom Santorum refused to identify.

Traynham, in an interview with The Philadelphia Inquirer, offered another reason why the people who paid for the children's trip should not be named: "The four kids are off-limits, and I don't think that's really necessary to go into the travel arrangements of four small children."

Since calling on Romney to release his tax returns, Santorum has promised to release his own, yet he still has not done so.

More on Santorum's 2012 campaign:

Another Southern Win
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Rick Santorum picked up bragging rights and nine more delegates with a win in Louisiana, but still lags far behind Mitt Romney.

The Red, White & Blue Fund, which supports him, has laid out a memo showing how he still hopes to take the nomination.

Santorum's next important battlegrounds come in Wisconsin and his home state of Pennsylvania.

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