During the 2016 campaign, Donald Trump egged on his supporters when they chanted “Lock her up!” about Hillary Clinton at nearly every one of his rallies. He repeatedly went after his Democratic opponent for her use of a private email server as secretary of state, saying she endangered national security and potentially let U.S. secrets get out.

Crooked Hillary Clinton and her team "were extremely careless in their handling of very sensitive, highly classified information." Not fit! — Donald J. Trump (@realDonaldTrump) July 6, 2016

Hillary Clinton should not be given national security briefings in that she is a lose cannon with extraordinarily bad judgement & insticts. — Donald J. Trump (@realDonaldTrump) July 30, 2016

Lyin' Hillary Clinton told the FBI that she did not know the "C" markings on documents stood for CLASSIFIED. How can this be happening? — Donald J. Trump (@realDonaldTrump) September 4, 2016

But Trump himself has absolutely no idea how to handle classified information. (And he apparently also doesn’t know that C stands for “confidential.”)

The Washington Post reported Monday that Trump disclosed “highly classified” information to the Russian foreign minister and ambassador during a White House meeting last week. The material reportedly came from a source who knows about the inner workings of ISIS and was so sensitive it hadn’t even been shared with U.S. allies and many people within the U.S. government.

“Donald Trump still believes someone who gave classified national security secrets to our adversaries is unfit to be President, right?” said Jesse Ferguson, who served as a spokesman for the Clinton campaign.

Despite what he said on the campaign trail, Trump has never really seemed to grasp the nuances of foreign policy ― and he often didn’t show much interest. After he won the election, Trump refused to go to the briefings offered by the intelligence community every day, saying he didn’t need them because he was a “smart person.”

“You know, I’m, like, a smart person. I don’t have to be told the same thing in the same words every single day for the next eight years. Could be eight years — but eight years. I don’t need that,” Trump said in December.

Officials told The Washington Post that, even though the National Security Council still prepares detailed, multi-page briefings for Trump to deal with foreign leaders, “he has insisted that the guidance be distilled to a single page of bullet points — and often ignores those.”

“Every day we get closer to testing Trump’s theory about what would happen if he shot a man on Fifth Avenue in broad daylight. To the foreign ally he betrayed, this may already be the equivalent of that,” said Brian Fallon, who was the Clinton campaign press secretary, referring to Trump’s campaign statement that his voters would stick by him no matter what he did.

Trump’s advisers also relentlessly attacked Clinton for her use of a private email server.

You know, I’m, like, a smart person. Donald Trump

Michael Flynn, Trump’s former national security adviser who resigned after lying about his contact with the Russian ambassador before Trump took office, said Clinton should be in jail for what she did.

“You know why we’re saying that [lock her up]? We’re saying that because if I, a guy who knows this business, if I did a tenth, a tenth of what she did, I would be in jail today. So ― so, Crooked Hillary Clinton, leave this race now!” Flynn said in his speech at the Republican National Convention.

Even as president, Trump has continued to rail against leaks coming from within the federal government, arguing that people who reveal classified secrets should go to prison.

“Classified. That’s classified,” he said in a recent interview with Time magazine. “You go to prison when you release stuff like that. And who would release that?”

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