WASHINGTON (AP) — Revelations that President Donald Trump is personally liable for more than $400 million in debt are casting a shadow over his presidency that ethics experts say raises national security concerns he could be manipulated to sway U.S. policy by organizations or individuals he’s indebted to.

New scrutiny of Trump, who claims great success as a private businessman, comes after The New York Times reported that tax records show he is personally carrying a staggering amount of debt — including more than $300 million in loans that will come due in the next four years.

Sen. Elizabeth Warren, D-Mass., was blunt about the potential implications. “He may be vulnerable to financial blackmail from a hostile foreign power and God knows what else,” said Warren, a frequent Trump critic.

The Times said the tax records also show that Trump did not pay any federal income taxes in 11 years between 2000 and 2018, raising questions about the fairness of a president — who purports to be a billionaire — paying less in taxes than most Americans.

The politically damaging revelations about Trump’s tax avoidance, however, are perhaps less concerning than word the president is holding hundreds of millions of dollars of soon-to-mature debt, ethics experts said.

“Americans should be concerned about the president’s debt because it’s a national security risk for our country,” said Donald Sherman, deputy director of the nonprofit government watchdog group Citizens for Responsibility and Ethics in Washington (CREW). “This is information that the president has aggressively and repeatedly tried to keep away from the public.”

Trump, citing an ongoing Internal Revenue Service audit, has refused to follow the post-Watergate precedent set by other presidents of releasing his tax returns, so the complexities of his financial interests and who he does business with have remained opaque. He’s fighting ongoing court battles with New York’s attorney general, Manhattan’s district attorney and two House committees who want the records.

Richard Painter, who served as chief ethics attorney in Republican George W. Bush’s White House, also noted that Trump-owned companies have declared bankruptcy six times, raising the question: Why have lenders been willing to keep risking loans of such enormous amounts?

“Why would banks assume the risk on these loans?” Painter said. “Or did someone else quietly assume risk of that loan for the bank to make it happen?”

Trump, according to his latest financial disclosure statement, reported that he had 14 loans on 12 properties.

One lender, Germany-based Deutsche Bank, continued to do business with Trump even after he defaulted in 2008 on a loan for his Chicago hotel and condo development. Trump filed suit against the bank and others whom he blamed for his inability to repay.

But Deutsche Bank’s private banking division continued to lend to Trump, including $125 million to finance the purchase and renovation of his Doral golf resort in 2012, according to previous disclosures.

Trump on Monday suggested that his debt load is hardly unusual in comparison with his assets, claiming in a tweet that he’s in fact “extremely under leveraged.”

“I have very little debt compared to the value of assets,” he wrote, adding that he may release a financial statement that spells out all assets, properties and debts.

Trump during an appearance on Monday ignored a reporter’s question about when he might release such a statement, and the White House would not comment on when he might follow through. He said repeatedly before his election that he would release his actual taxes but never has.

Kathleen Clark, a government ethics expert at Washington University in St. Louis, said that a separate financial statement from Trump would shed little light on his business dealings if he does not disclose who his business partners are in his various holdings.

“The Trump Organization consists of hundreds of LLCs (limited liability corporations) that have been listed on his financial disclosure forms,” Clark said. “One of the things that Trump has benefitted from and that oligarchs and money launderers benefit from is opaqueness of LLCs, … the ease of which individuals can hide their assets, can hide their financial interests.”

Trump refused to divest his business interests after his 2016 victory, and left day-to-day operation of his family’s real estate and other holdings to his sons Donald Jr. and Eric. Still, the president has benefitted personally from U.S. and foreign government activity at his properties since his election and hasn’t shied away from promoting his hotels and golf courses.

Republicans have held at least 88 political events at his properties, the president has visited his hotels and golf courses more than 500 times, and at least 13 foreign governments have held events at Trump establishments, according to a tally by CREW.

The administration drew criticism last year when Vice President Mike Pence, while visiting Dublin for meetings, lodged at Trump International Golf Links and Hotel more than 180 miles away in Doonbeg, Ireland. And Trump scrapped a plan to hold a meeting of the Group of 7 world leaders at one of his Florida properties last year after bipartisan criticism.

In the runup to his 2016 election victory, Trump played down his bankruptcies as a smart business strategy and even referred to himself as the “king of debt.”