Democratic presidential nominee Hillary Clinton on Monday landed a solid blow upon her Republican opponent, Donald Trump, over his refusal to release his tax returns.

Trump claimed that as “soon as the audits are finished, it will be released.”

“You will learn more about Donald Trump by going down to the federal elections where I filed a 104-page, essentially, financial statement of sorts. The income is filed at $694 million for this past year. $694 million,” he added. “If you would have told me I was going to make that 15 or 20 years ago, I would have been very surprised. But that’s the kind of thinking that our country needs.”

Then Trump pivoted, saying he would release his tax returns “against my lawyers’ wishes. I will release them as soon as she releases her 33,000 emails.”

Clinton wasted no time in drilling down on Trump’s secrecy over his taxes.

“For 40 years, everyone running for president has released their tax returns, and you can go and see 39 or 40 years of our tax returns,” she said. “We know the IRS has made clear there is no prohibition on releasing them when you’re under audit. So you’ve got to ask yourself, ‘Why won’t he release his tax returns?’”

“First, maybe he’s not as rich as he says he is,” Clinton continued. “Maybe he’s not as charitable as he claims to be. Third, we don’t know all of his business dealings, but we have been told through investigative reporting that he owes about $650 million to Wall Street and foreign banks. Or maybe he doesn’t want the American people, all of you watching tonight, to know that he’s paid nothing in federal taxes.”

“The only years that anybody’s ever seen were a couple of years when he had to turn them over to state authorities, when he was trying to get a casino license, and they showed he didn’t pay any federal income tax,” she said.

“That makes me smart,” Trump shot back.

“So he paid zero,” Clinton continued, “that means zero for troops, zero for vets, zero for schools or health. And I think probably he’s not all that enthusiastic about having the rest of our country see what the real reasons are, because it must be something really important, even terrible, that he’s trying to hide.”

Trump has used various excuses over the last year to explain why he has decided to break a 40-year tradition of disclosure in American politics. Every presidential nominee since Jimmy Carter has released tax returns to the public.

Trump said in February that he couldn’t wait to release his returns, and that he would do so as soon as an audit of a few years’ worth of returns was finished. The following month, however, Trump quietly released a letter from his tax lawyers, in which they claimed the businessman was under a “continuous audit.” This paved the way for Trump to say he couldn’t release any returns at all.

But Trump’s excuses rang hollow, in large part because there is nothing in the law that prohibits individuals from releasing their tax returns to the public.

As the summer wore on, it became more obvious that Trump wasn’t releasing his tax returns because he was afraid voters wouldn’t like what was in them. He cited the example of the 2012 GOP nominee, Mitt Romney.

Romney “didn’t want to give his tax returns,” Trump said on Fox News in July. “He fought like crazy. … But let me tell you, Romney gave those tax returns and they were absolutely fine. He was destroyed. [Reporters] went through his returns, which were peanuts compared to what I have.”

Romney’s taxes revealed that the multimillionaire paid a very low tax rate, thanks to loopholes that favor the wealthy.

The issue of Trump’s tax returns has become more pressing in recent weeks, as new information has come to light about how deep Trump’s financial ties are to foreign companies and investors. His company, the Trump Organization, has more than 500 separate corporate entities under its umbrella, and scores of them are involved in developments overseas.

This complex web of real estate investments and licensing deals would cause a President Trump nearly constant conflicts of interest, as he directed U.S. policy at home and abroad. Trump has said that he would entrust his company to his adult children if elected.

“My children will run it along with my executives,” he said in June. “It’s a big company. My children will run it along with my executives, and just do a good job running it.”

But according to government ethics experts, handing Trump’s business interests to his children would not change the circumstances of any conflicts of interests. Under typical conflict of interest laws, the interests of Trump’s family — his children, siblings and his wife — would count as his own, leaving the real estate developer right back where he started.

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims — 1.6 billion members of an entire religion — from entering the U.S.