Among the early front-runners for the dumbest California law of 2019 is the first-in-the-nation legislation requiring presidential candidates to release their tax returns to be eligible for the primary ballot.

If it isn’t unconstitutional, it should be.

Let’s be clear: Presidential contenders should follow precedent and voluntarily release their tax returns. It’s important for all candidates, but especially for Trump, given the controversies surrounding his financial affairs. Refusing this basic transparency test should be a red flag for voters, but it shouldn’t prevent candidates from being on the ballot.

The president and the Republican Party filed suit in federal court last week, one week after Gov. Gavin Newsom signed the state’s new law requiring presidential candidates to submit five years of income tax filings by late November in order to be eligible for California’s March 3 primary.

The legislation, SB 27, by state Sen. Mike McGuire, D-Healdsburg, passed the Legislature on a party-line vote in July.

Trump’s lawyers called the California law “a naked political attack against the sitting president of the United States.”

They’re right.

At least former Gov. Jerry Brown had the good sense to veto a similar bill also authored by McGuire in 2017, saying it would set a bad precedent.

“Today we require tax returns, but what would be next?” Brown wrote in his veto message. “Five years of health records? A certified birth certificate? High school report cards? And will these requirements vary depending on which political party is in power?”

For the record, Brown refused to release his returns when running for governor in 2010 and 2014.

If California’s law keeps Trump off the ballot in 2020, Republicans likely will retaliate in kind with new laws in red states designed to keep the Democratic candidates they most fear off the primary ballot.

Following President Obama’s election in 2008, lawmakers in several states, who were trying to perpetuate myths about his origin, considered laws requiring proof that a candidate was a natural-born citizen.

McGuire said that he consulted with constitutional scholars when writing the California’s tax-return legislation. Election-law experts disagree on whether it will pass constitutional muster. Some argue the Constitution gives states wide latitude to shape their primary elections. Opponents say the courts should kill the law because it disenfranchises voters whose preferred candidates meet federal standards.

As eager as many Americans are to see Trump’s tax returns, this is the wrong way to go about it. It won’t keep him from being the GOP nominee in November.

Congress is suing the Internal Revenue Service in an effort to get six years of Trump’s tax returns. Federal tax code grants the chairmen of Congress’ tax-writing committees power to request tax information on any filer. Congressional lawyers note that the same type of request was granted in the 1970s when Congress sought to obtain President Nixon’s tax returns.

The action by the House Ways and Means Committee may not be as politically satisfying as California’s blatant ploy. But it’s a far more appropriate approach to forcing Trump to reveal his tax returns.

— The (San Jose) Mercury News