A preliminary review of the thousands of pages of Donald Trump’s tax returns released by a key congressional committee on Friday confirms that the former president was using business losses in the tens of millions of dollars to reduce his annual tax liability, in some cases all the way down to zero. 

While one of Trump’s main businesses was found guilty of criminal tax fraud earlier this month, Trump himself has so far not been accused of doing anything illegal with his taxes and personal accounting.

But that’s raising more urgent questions about the fairness of the U.S. tax code and tax regulations, which number in the millions of words and in the case of Trump proved effectively unenforceable.

Advocates for tax reform say that a shift in mindset is needed, that a flawed conception of taxation as punitive and economically destructive is what allows for the sort of serial tax avoidance on display in the Trump tax returns.

“With the release of Donald Trump’s tax returns we have learned that he did not pay any federal income taxes [in some years],” Frank Clemente, director of tax advocacy group Americans for Tax Fairness, said in a statement to The Hill.