(CNN) The Justice Department has released a trove of decades-old internal legal memos concluding the President should be legally barred from appointing a relative to a position in the White House, shedding new light on just how sharp a departure the department's more recent interpretation of federal law under the Trump administration compares to past practice.

When the Justice Department concluded on Inauguration Day 2017 Jared Kushner could serve in his father-in-law's administration without violating anti-nepotism laws, legal experts scratched their heads at the ruling.

Monday's newly released memos -- first reported by Politico , which filed a Freedom of Information Act request -- illustrate why the reversal was so stark.

Dating back to the Nixon administration, the Justice Department provided an unbroken chain of advice: federal law forbids the President from appointing a relative "to a civilian position in the agency ... over which (the official) exercises jurisdiction or control," including a temporary or permanent appointment to the White House staff.

"You have asked for our opinion on the question whether the President could appoint Mrs. (Rosalynn) Carter to be Chairman of a Commission on Mental Health proposed to be established in a forthcoming Executive Order," wrote acting Assistant Attorney General John Harmon in a February 1977 memo to a lawyer in the Carter administration. "It is our opinion that he may not."

Harmon added that the statutory prohibition should apply "whether or not the appointee will receive compensation."

A similar finding came from Edwin Kneedler in 1977, who concluded that President Jimmy Carter could not appoint his son to an unpaid position on the White House staff.

"As pointed out in our memorandum . . . regarding Mrs. Carter," Kneedler explained, "it makes no difference that he would serve without compensation."

Yet deputy assistant attorney general Daniel Koffsky, a longtime career attorney at the Office of Legal Counsel at the Justice Department, reversed course in January, finding the anti-nepotism law covers only appointments in an "executive" agency and that the White House Office is not such an agency under the law.

"In choosing his personal staff, the President enjoys an unusual degree of freedom, which Congress found suitable to the demands of his office," wrote Koffsky, relying on a separate law giving the President broad authority to hire his staff.

Despite the criticism levied by ethics experts, Kushner's lawyer said back in January that the new opinion was justified.

"We believed that we had the better argument on this," Kushner's lawyer Jamie Gorelick said in a statement at the time. "The Office of Legal Counsel of the Justice Department -- in an opinion by a highly regarded career Deputy Assistant Attorney General -- adopted a position consistent with our own."