During a speech in Ohio on Tuesday, the former Secretary of State blasted the New York businessman for refusing to release his tax returns, suggesting that it may be because he’s payed very little in taxes, or because “he isn’t a rich as he claims.”

Donald Trump’s wealth is back in the news this week after Federal Election Commission filings show that his campaign has just $1.29 million in the bank, versus a Clinton war chest of $42 million. Some pundits are suggesting that this is evidence that Trump isn’t as wealthy as he claims, otherwise he would be spending more on his campaign during a critical period in which voters are forming their impressions of the two candidates.

In May, Fortune examined Trump’s latest personal financial disclosure forms and estimated that his true wealth is roughly $3.9 billion. That was up from our previous estimate of $3.7 billion, based on earlier filings, but still well south of the “TEN BILLION DOLLARS” Trump’s campaign claims. Because Trump’s businesses are largely privately held, and because he refuses to release his tax returns, it’s impossible to know for sure his true net worth.

That said, we do know that Trump has large ownership stakes in Manhattan office buildings like 40 Wall Street, Trump Tower, and 1290 Avenue of the Americas, all of which are worth hundreds of millions of dollars. The fact that he has been fairly stingy in donating to his own campaign may be because this sort of wealth is highly illiquid, unlike those who’s riches are in the form of stocks and bonds.