Pepe Cardona is one of the largest players in Mexico’s violent and tumultuous casino trade. In 2007, he survived an assassination attempt that was attributed to members of organized crime. The State Department cable, which was part of the cache made public by WikiLeaks, said he was suspected of illegally funneling $5 million into Mexican political campaigns in 2006.

Multiple messages left for Alberto and Carlos Cardona over several days were not returned. A sister-in-law, Sarah Westall of Minnesota, said in a telephone interview that it would be wrong to tar other members of the family with the negative publicity surrounding Pepe Cardona.

Ms. Westall, who is married to another Cardona brother, Gabriel, said Alberto and Carlos took up Democratic fund-raising because their extended family had long been involved in helping the Latino community and because they supported the president. There were no other reasons beyond those, she said. “I understand that it looks real bad,” she said. “But the rest of the family are really good people. Pepe is actually a good person too.”

Whatever the family’s motivation, the president cannot pardon someone for state crimes. On Monday, Democratic fund-raisers who have had encounters with Alberto and Carlos Cardona expressed surprise upon learning about their family history. Manuel Sanchez, a Chicago lawyer who is deeply involved in Latino outreach for the Obama administration, said he first met them in December at a finance committee meeting for the president’s campaign in Washington.

He said he had been told that they were involved in “marketing and advertising.” They impressed him as “very smart young guys who wanted to support the president,” he said.

“I did get the distinct impression that both of them are very well-to-do and successful in their businesses,” Mr. Sanchez said, adding that he “had no idea” they had a brother in Mexico or what his background was.