Donald Trump owes his presidency to the Electoral College more than any other factor, even Russian interference. This constitutional quirk also gives a hint of irony to an unusual bill passed earlier this week by Maryland’s Democratic-controlled State Senate.

The senators voted 28-17 on Monday, largely along party lines, to require presidential candidates to file copies of their tax returns with the state board of elections two months ahead of Election Day, so the filings can be made public. Failure to comply would result in the candidate’s removal from the state ballot that November.

The bill’s target is clear: Trump, who broke a forty-year precedent by refusing to release his tax returns during his campaign. Now that he’s in the White House, the most reliable accounting of his wealth and debts is something of a state secret: the Internal Revenue Service keeps his returns (and those of other presidents) in a locked and guarded room that even the agency’s commissioner can’t access alone. States like Maryland are now working to fill that transparency void—and may be on solid constitutional footing to do so.

Rick Hasen, a U.C. Irvine law professor who specializes in elections, explored the possibility in a March 2017 article for Politico. At the time, he noted that almost half of the state legislatures were considering some kind of measure that would compel future presidential candidates to disclose their tax returns. The optimal path for this reform is through each state’s power to determine how it selects its presidential electors.

Today, the states invariably leave the choice to the voters. But the earliest American presidential elections saw a variety of methods ranging from popular vote to selection by state legislators. There’s no formal barrier that prevents a return to the old ways, either. “In other words, if the California or Texas state legislature wanted to directly choose the state’s presidential electors in 2020, the state could do so,” Hasen noted.