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California is trying to force presidential norms on Donald Trump.

On Monday, lawmakers from California joined their New York counterparts in supporting legislation that would legally require presidential candidates to release their tax returns to qualify for Electoral College votes in their states. The TRUMP (Tax Returns Uniformly Made Public) Act has a strong chance of passing in California and could be implemented before the next presidential election.

Trump has ignored repeated calls to release his tax returns, stoking concerns about conflicts of interest in his foreign policy and nepotism in his administration. He is the only president in recent history never to release his tax returns to the public.

Trump’s supporters may rejoice at watching the president-elect shirk long-established norms surrounding his office. But Trump’s actions go beyond shaking up politics as usual. Such conventions are not useless elements of bureaucracy, but cornerstones of a stable democracy. They have not been protected by law in the past because there has been no need to carve them in stone as hard-stop obligations. But if Trump can’t be coaxed into abiding by them, it’s time that legislators took a strong-handed approach. If red or purple states follow, then he might begin to feel the pinch.