What did Donald Trump do today?

He made his final appeal to keep his tax returns secret.

Trump filed an appeal with the Supreme Court today in what will be, from a legal perspective, his last chance to keep his personal and business tax returns from law enforcement officials. 

There is overwhelming evidence that Trump got much of his inheritance from his father, amounting to the present-day equivalent of almost half a billion dollars, through tax fraud. He can no longer be prosecuted for those apparent crimes because the statute of limitations has expired, although the threat of an internal investigation forced his sister, a federal judge, to retire.

Congress is (separately) attempting to exercise its legal right to review his personal tax returns because Trump is widely suspected of having participated in money laundering for Russian oligarchs, among other crimes that would make him vulnerable to blackmail. But the present case, brought by the Manhattan District Attorney's office, is about his business returns. Trump is suspected of having laundered hush-money payments to women he had sex with through the Trump Organization.

There is a legal theory that a sitting president cannot be indicted, although this has never been tested in the courts. It is the prevailing interpretation at the Department of Justice, which is why the special counsel Robert Mueller did not seek Trump's indictment. Trump's argument in the tax case, which every lower court has emphatically rejected, is that not only can he not be indicted, he can't even be investigated, no matter how overwhelming the evidence is that he committed a crime.

In other words, Trump is arguing that while he remains in office, he is above the law, and that impeachment is the only remedy for a lawbreaking president. (He's also said it's illegal to impeach him because he hasn't been convicted of crimes.)

Neither the District Attorney nor Congress would be permitted to make Trump's tax returns public, except for anything that might be introduced as evidence in a criminal trial. Trump is the only president or presidential candidate since Richard Nixon to refuse to let the public verify that his finances are legitimate.

Why does this matter?

• Presidents are not above the law.