April 15 marks the traditional date that Americans know as Tax Day. Typically, the day raises loud groans from all of us taxpayers as we file our taxes (though groaning will be heard this year on Tuesday, April 18, when 2016 returns are due). But April 15 this year also marked a day of national uprising against an attack on the basic transparency and trust that should exist between the American people and the president of the United States.

We stand with the Tax Day protesters calling for President Trump to release his tax returns, and we are working on a bill to make sure no president can refuse to release his or her returns again. President Trump’s disregard for this tradition is alarming because our conflict of interest laws do not apply to the Office of the President. It is alarming because this administration seems set on undermining every norm called for by an ethical and accountable government. It is alarming because the American people have been left in the dark.

Ever since Jimmy Carter ran for our nation’s highest office, every major presidential candidate has released his or her tax returns in an effort to be transparent and accountable to the people they wish to serve. The decision to do so was not about partisan politics — Republicans and Democrats alike have released returns — but about making our democracy stronger. But President Trump broke with this time-honored tradition by refusing to release his tax returns — even though he had promised the American public that he would.

We will never know what financial connections and potential conflicts of interest exist between President Trump’s business interests and foreign governments. Or if he’s taking actions to benefit his business partners or lenders. Or if the tax reform he is undertaking is aimed at benefiting the American people or his own balance sheets. In short, the American public will never know if their president is putting his own interests before those of the nation.

As the Republicans in Congress have shown little interest in pursuing disclosure from the Trump administration, it is up to state legislators to seek this basic level of transparency.

That is why we have introduced SB149, the Presidential Tax Transparency and Accountability Act. This straightforward bill simply says anyone who wants to appear on the California presidential primary ballot must submit five years of personal tax returns to the California secretary of state.

Once it becomes law, if President Trump ever wants to appear on the California ballot again, he will need to do what presidential candidates have done for decades before him — be open and honest about his finances with the American people.

Transparency and disclosure are nonpartisan issues. In the end, yes, we want to hold Donald Trump accountable, but this bill is bigger than just one person. It’s about standing strong for American constitutional values and time-honored traditions that have made our democracy stronger.

SB149 is working its way through the California State Senate, with a hearing on Tuesday in the Elections and Constitutional Amendments Committee. But even as this bill moves forward, the Tax Day protesters need to be heard by the president. The level of distrust engendered by his obfuscation and secrecy is harming his presidency, and it is harming the American people. He should release his returns now, or California will do it for him.

State. Sen. Mike McGuire, a Democrat, represents the North Bay and North Coast. State Sen. Scott Wiener, a Democrat, represents San Francisco and northern San Mateo County.