This week, the Trump transition team announced that President-elect Donald Trump‘s son-in-law, Jared Kushner, would serve as a senior advisor in his White House.

The move has been rumored since even before Trump won the election back in November. Kushner, husband to Trump’s eldest daughter Ivanka and a New York real estate magnate in his own right, was an instrumental, behind-the-scenes player in Trump’s campaign.

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Kushner has frequently been spotted with the president-elect following Trump’s upset victory — including days after the win when he accompanied Trump to visit President Obama in the White House. He and Ivanka are also planning to move to Washington, D.C. once Trump’s presidency begins.

Though Kushner’s appointment does not require Senate confirmation, it is a controversial one: Anti-nepotism laws forbid the hiring of relatives to Cabinet positions, but are less clear on whether they can be appointed to White House staff roles.

In American history, anti-nepotism laws are actually a relatively recent development: They were put into place in 1967 by then-President Lyndon B. Johnson not long after one of his predecessor’s appointments raised eyebrows.

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After his election in 1960, John F. Kennedy famously appointed younger brother Robert F. Kennedy to the position of attorney general, despite the fact that he had no experience in either state or federal courts. Although the appointment was criticized at the time, according to Time the president joked, “I can’t see that it’s wrong to give him a little legal experience before he goes out to practice law.”

The law, formally titled The Federal Anti-Nepotism Statute but often nicknamed the “Bobby Kennedy Law,” was put in place in 1967, under Kennedy’s successor and former vice president, Lyndon B. Johnson. It was an unspoken truth in Washington that Johnson resented RFK’s appointment. With the attorney general and the president sharing an obviously close, brotherly relationship, Vice President Johnson often reportedly felt he was left on the outskirts. Johnson reportedly even used to call RFK a “snot-nosed son of a bitch.”

The anti-nepotism statue was passed as part of the Postal Revenue and Federal Salary Act of 1967.

What exactly the law does and doesn’t prohibit hasn’t always been clear, Jonathan Turley, a professor of law at the George Washington University Law School, told The Daily Beast.

“I think one has to draw the distinction between actions that are unwise and actions that are unlawful,” Turley said of Kushner’s appointment. “The anti-nepotism law has long suffered from a glaring ambiguity.”

Richard Painter, President George W. Bush’s former chief ethics lawyer, agrees. He told The Daily Beast that there’s space for differing opinions on the subject.

“I don’t think the answer is cut and dry on anti-nepotism,” Painter told The Daily Beast. “There’s some room to disagree on that, and I don’t know what the right thing is,” he said, referring to the anti-nepotism statute.

One president, however, managed to get around the law since it was put in place: Bill Clinton, who appointed wife Hillary to lead his administration’s health care reform strategy. How? Back in 1993, two federal judges ruled that though the law applied to Cabinet appointments (think secretary of state or yes, attorney general) or paid positions in government, it didn’t apply to White House staff.

“We doubt that Congress intended to include the White House or the Executive Office of the President” D.C. Circuit Judge Laurence Silberman wrote in the 1993 decision, according to The Daily Beast. “So, for example, a President would be barred from appointing his brother as Attorney General, but perhaps not as a White House special assistant.”