Democrats have redoubled their efforts to force President Trump to release his federal tax returns by threatening to keep him off the 2020 ballot in deep-blue states, to which he might say: So what?

Seventeen states have seen bills introduced this year that would require presidential candidates to turn over their tax returns as a condition for ballot access, and such measures have cleared one legislative chamber in at least four states.

For the Trump campaign, however, there may be worse fates than being left off the ballot in liberal enclaves like California, Hawaii and Illinois, where the mandatory tax-return bills are making headway, given that no Republican presidential contender is likely to prevail there.

“In theory, he [Trump] could really push this, and he could be disqualified from the state ballots, and it wouldn’t necessarily affect the Electoral College vote at all,” said University of Denver political science professor Seth Masket. “Because those were states he wasn’t going to win anyway.”

Before that happens, the bills must first win passage, and with many legislative sessions winding down, no such measure has reached a governor’s desk.

In Washington state, the Senate passed a bill last month requiring presidential contenders to release five years’ worth of tax returns before appearing on a primary or general election ballot, but the measure died without House approval when the session adjourned at midnight Sunday.

Other states still have time to wrestle this year with whether requiring presidential hopefuls to disclose their Form 1040s represents a commonsense transparency measure, or a politically motivated attack on Mr. Trump certain to be struck down the courts.

Josh Blackman, associate professor at the South Texas College of Law, said the bills “are inconsistent with Supreme Court precedent.’

“As a general matter, states cannot impose additional requirements for federal officers,” Mr. Blackman said. “For example, states cannot impose term limits on members of Congress. Or require that the President be 40 years old, instead of 35, as the Constitution requires.”

The only way to mandate tax returns would be through a constitutional amendment to Article II, requiring ratification of three-fourths of the states, said Jenna Ellis, a fellow in constitutional law at the Centennial Institute.

“Neither Congress nor the state legislature can unilaterally add a requirement and bind the Electoral College,” said Ms. Ellis, a member of the Trump 2020 advisory board.

Then again, states typically require federal candidates to clear some sort of bar before their names are placed on the ballot, such as submitting a certain number of valid signatures from voters or paying a filing fee.

“My impression is that constitutionally, this is defensible,” said Mr. Masket. “The Constitution gives pretty broad discretion to the states as to how to run their own elections and how to qualify for the ballot.”

If states can require filing fees and signatures, he said, “then it would seem like a tax disclosure isn’t a problem.”

Even so, the specter of states adding ever-more qualifications for candidates was enough to convince then-California Gov. Jerry Brown to veto a mandatory tax-return bill in 2017, saying he worried about setting a “‘slippery slope’ precedent.”

“Today we require tax returns, but what would be next?” he asked 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?”

Former New Jersey Gov. Chris Christie nixed a similar bill the same year, calling it “politics at its worst.” Senate Democrats haven’t given up, however, approving in February a bill requiring five years’ of tax returns and also prohibiting electors from voting for a candidate who refuses to do so.

Voters “must know, unequivocally, that the person they vote for is invulnerable to blackmail, coercion or intimidation of any kind due to financial liabilities,” said New Jersey Senate Majority Leader Loretta Weinberg in NJ.com.

Not surprisingly, the state measures have split along party lines, with Democrats, backed by progressive advocacy groups like Indivisible, in favor and Republicans against.

“It’s clearly unconstitutional. It’s clearly targeted at the President of the United States,” Illinois state Sen. Dale Righter, a Republican, told the Illinois News Network.

He pointed out that the bill, which passed the state Senate April 13, has no such requirement for gubernatorial or legislative candidates in a state dominated by Democrats.

“Notice that the bill doesn’t require the disclosure the release of tax returns by, let’s say, a candidate for governor, or a candidate for [House] Speaker, or a candidate for Senate President,” Mr. Righter said. “I think that’s a not-very-well-veiled attempt to keep President Trump off the ballot.”

Hawaii legislators have approved a similar bill in the state Senate, while a reintroduced California measure has cleared two state Senate committees.

In Mr. Trump’s home state of New York, Democrats are trying a different approach with a bill that would authorize the state Department of Taxation and Finance to release returns to a congressional committee. A state Senate committee voted Tuesday to advance the measure to the floor.

“If Washington won’t take the lead and provide accountability for the American people, New York will,” tweeted Democratic state Sen. Brad Hoylman, the bill’s sponsor.

House Ways and Means Committee chairman Richard Neal requested April 3 six years of Mr. Trump’s personal and business tax filings from the IRS.

There is no requirement to disclose tax records before running for president, but since 1976, every major presidential candidate with the exception of former President Gerald Ford has released some federal tax filings, according to PolitiFact.

Sign up for Daily Newsletters Manage Newsletters

Copyright © 2020 The Washington Times, LLC. Click here for reprint permission.