(CNN) Earlier this week, California Gov. Gavin Newsom (D) signed into law a measure that would force President Donald Trump to release his tax returns in order to qualify for the 2020 ballot in the nation's most populous state.

Which raises all sorts of questions. Can a state make this sort of requirement to qualify for the ballot? What happens if the incumbent president isn't on the ballot in all 50 states?

I asked all those questions -- and more -- of John Myers , Sacramento bureau chief of the Los Angeles Times. Our conversation, conducted via email and lightly edited for content.

Cillizza: Start from the beginning. Who introduced this legislation and when?

Myers: This proposal first surfaced in the days after President Trump took office in 2017. Two Democratic state legislators from Northern California, still fuming over Trump's refusal to release his tax returns during the 2016 campaign, made it clear they wanted to force the issue of ballot access in the California Legislature. Their effort has largely been a partisan battle ever since -- with Democrats in the statehouse in Sacramento in support but the small number of Republican legislators left in office (their ranks continue to shrink in the Golden State) insisting it was little more than a political stunt.

The only real Democratic dissonance -- and it was notable -- came from then-Gov. Jerry Brown. The long-serving governor didn't veto many bills that came to his desk, but when he did, it was with a unique 'let's get real' reaction to the more provocative proposals that came his way. I think you'll see Brown's 2017 veto of a substantially similar proposal quoted again and again as this legal debate begins.

In part, Brown wrote:

"Today we require tax returns, but what would be next? 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?"

The state legislators behind the plan, not surprisingly, thought Brown was wrong. And when Gov. Gavin Newsom took office this past January, they saw the chance to try again. The one significant difference between the 2017 effort and the law signed by Newsom is a provision -- apparently added after conversations he had with the bill's authors -- that includes candidates for California governor in the tax-disclosure process. (Fun fact: While Newsom released his tax returns during the 2018 campaign, Brown did not do so in either his 2010 or 2014 gubernatorial efforts.)

Cillizza: Newsom was very vague about whether he would sign the bill into law throughout the process. Did he give any indication what tipped the scales?

Myers: I think there was a pretty strong feeling that while Brown's tendency was to say 'no' to the idea, Newsom's was to say 'yes.' So it seemed to be more about whether solid legal arguments could be made to him that it would pass muster with the courts. And in his view, and that of the Democrats who wrote it, they have it. A variety of constitutional lawyers think there's an opening (and I'm not a lawyer!) provided by the Constitution's allowance that state legislatures can decide how they choose electors for president. Of course, others believe the rules already delineated -- age, place of birth -- are as far as anyone can go. Everyone knew this was headed for the courts. So now we wait.

Cillizza: How much of this is about Newsom escalating California's feud with Trump and how much of it is about the governor's genuine desire to force transparency out of politicians?

Myers: That's a tough one to answer because I think it's fair to say both are at play. My hunch, in talking to so many people about this issue through the years, is that the process of releasing tax returns had become an accepted canon of presidential campaigns after 40 years of pretty consistent releases by major party nominees. Trump -- both because he refused and because his financial dealings appeared to be so complicated -- broke that mold in a way that made some in politics realize there could be serious issues at play about conflicts of interest when it comes to a president's dealings with national and international issues.

Then again, Newsom is an unabashed critic of almost everything Trump says and does. And he frequently took shots at the President's tax return refusal prior to this legislation being introduced in the California Capitol. I'm sure he relished the chance to try and hold Trump's feet to the fire.

I will say, though, that Newsom knows he could be walking a fine line. While he and the President often spar on social media (and the President criticized Newsom on Thursday during his Ohio rally), Trump has been pretty consistent in green-lighting disaster aid requests from California for wildfires and the recent series of earthquakes in Southern California. There remain fears that Trump will retaliate in some way.

Cillizza: This law is headed for a major legal fight. What's the process -- and timeline -- for the inevitable Republican appeal?

Myers: I think it's likely to get challenged first by a fringe candidate or minor political party. We've heard rumblings this week that a challenge from those corners is coming soon. But yes, the real show will be the assumed challenge from either Trump's campaign or from the Republican National Committee.

And timing really is a big deal: this bill was passed with what's known as an "urgency clause," meaning it takes effect immediately. (Most state laws in California do not.) Add to that the fact that California moved its presidential primary to March 3, 2020 -- which means the decisions about who does, and doesn't, qualify for the ballot will be made this fall. So I would expect we'll see substantial legal challenges filed soon in a federal court. Again, I'm not a lawyer, but I could certainly see this making its way to the US Supreme Court; I'm confident California won't back down should the state lose in the early rounds. And I doubt the President would back down, either.

Cillizza: Finish this sentence: When Gavin Newsom runs for a 2nd term as governor in 2022, the tax return law will be _______________." Now, explain.

Myers: That's a dangerous prediction to make! The one thing I'm most curious about is whether the law is blocked from taking effect for 2020 -- because of the very short timeline for the election process -- while the courts take their time to fully consider its legality. So perhaps the answer is "still being debated in the courts," though I'm not prepared to make that guess, either. (Fortune telling and journalism don't mix.)

Instead, I will say this: "The tax return law will be still hotly debated as to whether it was the right or wrong thing to do." I think it's raised a fascinating set of questions about why voters aren't entitled to as much information as possible about possible conflicts involving their elected officials. A number of GOP state legislators insisted the California law be broadened to include candidates for the state legislature (candidates for Congress might again land the issue in court). So I'll be curious to see if that takes root, or other efforts to force more transparency about candidates. If so, we may look back at this California law as the start of a nationwide discussion about truth in politics.