Updated

There's more trouble ahead for President Obama's nominee to lead the federal agency in charge of airport security.

Seven Republican senators on Wednesday wrote to the White House demanding information about the conflicting accounts nominee Erroll Southers gave Congress over background checks he ran on his then-estranged wife's boyfriend two decades ago.

Sen. Jim DeMint, R-S.C., previously had held up Southers' confirmation over concerns that he would unionize screeners at the Transportation Security Administration. Even after the failed bombing of a Northwest Airlines flight on Christmas led lawmakers to call for Southers' swift approval, DeMint stood by his objections.

The questions raised about the background checks added to his concerns -- DeMint joined six other senators in raising the issue with the White House.

"It's just part of a pattern of we are not vetting these candidates clearly," DeMint told Fox News. "I think more and more senators are concerned that this is not the kind of person we want leading, probably at the most vulnerable point we are as a nation as far as keeping our people secure."

Southers wrote to senators last week clarifying "inconsistencies" in his recollection of the background checks. The former FBI agent originally wrote in an October affidavit to a Senate committee that he asked a San Diego police employee to run a background check on his estranged wife's boyfriend and was censured by the FBI 20 years ago for it. He called it an isolated incident.

But after the committee approved his nomination and sent his name to the Senate, Southers wrote back and said that he actually personally ran background checks twice.

The GOP senators wrote Wednesday that it appears Southers "submitted erroneous, and possibly misleading, information regarding ethical violations," and posed a string of questions to the administration.

The White House reportedly said it did not know of discrepancies in his account until November but that the president stands behind the nominee.

Senate Majority Leader Harry Reid said after the Christmas Day attempt that he will cut off debate on Southers when Congress returns so that "the president has another key member of his national security team in his place."

While Democrats have criticized DeMint for putting up hurdles when the TSA is about to undergo changes in response to the Christmas incident, DeMint said the new information that has emerged validates his actions.

"I'm glad that I slowed this process down because now we're finding out a lot of things that should have been found out before he went through committee," he said.

The Associated Press contributed to this report.