Many constitutional law experts, former Democratic Gov. Jerry Brown and the California Republican Party are now all officially entitled to say, “I told you so.”

This morning the California Supreme Court unanimously struck down a new state law that would have required presidential candidates to publicly disclose their tax returns before appearing on the primary ballot.

He told you so.

Passed by the supermajority of Democrats in California’s Legislature and signed by new Democratic Gov. Gavin Newsom, the law was the statutory embodiment of California’s place at the front of the anti-Trump “Resistance.” It was a blatant dig at the GOP president — and one that generated plenty of national media attention.

But to some constitutional law scholars, the law was also obviously unconstitutional. Gov. Brown shared those concerns when he vetoed identical legislation in 2017.

Trump declined to release his tax returns during the 2016 presidential campaign, breaking with a precedent set in 1976 by President Jimmy Carter following the Watergate scandal.

“First, it may not be constitutional,” Brown wrote in his veto message at the time. “Second, it sets a ‘slippery slope’ precedent. Today we require tax returns, but what would be next?”

All seven justices of California’s Supreme Court were similarly persuaded.

“The Legislature may well be correct that a presidential candidate’s income tax returns could provide California voters with important information,” wrote Chief Justice Tani G. Cantil-Sakauye, a Gov. Arnold Schwarzenegger appointee. But, she added, the state constitution makes clear “it is the voters who must decide” whether a presidential candidate’s refusal “to make such information available to the public will have consequences at the ballot box.”

At a hearing earlier this month, Justice Ming Chin, one of four Brown appointees, wondered whether California’s tax return ballot rule might encourage state legislators to saddle would-be candidates with “a laundry list of potential requirements.”

He also told you so.

The law was likely on pace to meet a similar end in federal court as well. Last month, a district court judge put enforcement of the law on hold, writing in his opinion that while he empathized with the “motivations” of lawmakers who passed the bill into law, “the Act’s provisions likely violate the Constitution and the laws of the United States.”

The U.S. Constitution sets forth a very limited list of qualifications for those hoping to be president: a candidate must be a natural-born citizen over the age of 35 who has lived in the United States for at least 14 years. For decades the U.S. Supreme Court has held that states can set “procedural” requirements about where, when and how elections can take place, but have been otherwise averse to adding to that list of requirements.

Past attempts by states to impose term-limit requirements on people running for Congress or to require candidates to list their race on the ballot have been struck down.

Supporters of the law argued that publishing one’s tax returns was just another administrative step, akin to a signature-gathering requirement or paying a filing fee.

The ruling in California’s highest court cannot be appealed, meaning over the legal battle filed by the California Republican Party is now over.

California lawmakers have a track record of supporting bills of dubious legality but irresistable political appeal.

As CalMatters reported last month, in 2015 the Legislature passed a law forcing anti-abortion “crisis pregnancy centers” to provide their clients with information about free or low-cost abortion services. The law was eventually struck down as a clear violation of the First Amendment and the state was required to fork over $2 million to cover the legal cost of their ideological foes — a boon to the very anti-abortion forces the state was seeking to hamper.

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