As if begging to be audited, the conservative public watchdog Judicial Watch Tuesday stepped up its assault on the the luxury vacations of the first family by suing the U.S. Secret Service to reveal the cost of the Obama's last Christmas vacation in Hawaii, estimated at more than $4 million.

The group's Freedom of Information Act lawsuit follows an earlier request to the agency for records detailing government costs for security and other services during the early January trip which the Secret Service acknowledged but didn't comply with.

Judicial Watch has in the past succeeded in obtaining travel documents for the first family, detailing the security expenses to protect the first family and their companions, revealing the costs to house the security and even uncovering the prices paid for magazines and snacks purchased for the first family.

The most recent Hawaii trip cost more than $4 million, with most of the money going to fuel and fly Air Force One, according to news reports. Local reports said that the first family rented a seaside home priced at about $7,500 a day and that multiple other houses were rented for security and staff.

White House Dossier reported that the first family's four vacations to Hawaii have cost "likely in excess of $20 million, and possibly much, much more." The Hawaii Reporter has suggested that the trips cost about $4 million each, "much of it attributable to the expense of taking Air Force One, at an hour rate of about $180,000, on an eighteen-hour round trip journey to Honolulu and back," added Judicial Watch.

In the past, Judicial Watch has revealed other Obama trip costs:

» August 2010, when Michelle Obama traveled to Spain with multiple friends and one of her daughters, the total cost to taxpayers was at least $467,555.

» June 21-27, 2011, when Michelle Obama along with her daughters and staff traveled to South Africa and Botswana, charges to the taxpayers for the aircraft and crew alone were $424,142.

» Presidents Day weekend in February 2012, when Michelle Obama and her two daughters vacationed in Aspen, Colo., charges to the taxpayers were $83,182.99.

"The Obamas' opulent vacation lifestyle is particularly objectionable during a time when government debt is out of control," said Judicial Watch President Tom Fitton. "President Obama is not king and his administration should stop ignoring the FOIA open records law and account to the American people the spending on his luxury vacations."

Fitton told Secrets on Monday that his group was audited by the IRS when it was probing the Clinton administration in 1998, and that one IRS official said, "What do you expect when you sue the president?"

His group is already planning to investigate the current IRS scandal.