President Trump speaks at the White House in Washington on April 12. (Nicholas Kamm/Agence France-Presse via Getty Images)

President Trump was the first major-party presidential candidate to refuse to release his income tax returns in more than 40 years. He won the election nonetheless, and has persisted in refusing to allow the public to see his returns.

Some government-reform advocates and anti-Trump activists have a new idea to force President Trump to release his returns: Prohibit Trump from appearing on state ballots if he seeks reelection in 2020. It’s a clever idea, even if it would not force disclosure for several more years (and is premised on the assumption that Trump plans to run again). But is this plan constitutional?

Harvard Law School Professor Laurence Tribe, joining with Norman Eisen and Richard Painter of Citizens for Responsibility and Ethics in Washington, believe that such measures would be constitutional. Writing on CNN.com, they argue that a state-level requirement that all candidates for public office release their income tax returns would be a permissible ballot-access requirement, even as applied to Trump. They write:

Our federal Constitution allows states to create ballot access requirements that ensure that the ballots for every office, including the office of presidential elector, are comprehensible and informative.

A line must of course be drawn between permissible ballot access laws and impermissible attempts to add qualifications to those specified in the federal Constitution. But our research and analysis lead us to conclude that tax return disclosure laws such as the one proposed in California resemble ballot access laws in structure, impact, and purpose much more closely than they resemble laws imposing additional qualifications for presidential office. …

Unlike prohibited qualifications, these laws do not impose substantive requirements on candidates beyond those imposed by the Constitution itself; that is, these laws do not limit which candidates may run for office based on any particular information in their tax return. Thus, they do not create an insurmountable barrier in advance to any set of individuals otherwise qualified under Article II of our Constitution. Instead, these laws require federally qualified candidates to comply with a relatively minor process of tax disclosure. That is something competing candidates can and should readily do in order to allow voters to make more informed judgments about those contenders’ characters or backgrounds.

Pepperdine University Professor Derek Muller is unconvinced. Writing in the New York Times, he argues that any such requirement is a bad idea and would likely constitute a constitutionally impermissible effort to impose additional qualifications for federal office. Focusing on one such ballot proposal in New Jersey, he writes:

The Supreme Court has repeatedly held that states can’t use the ballot as a political weapon. In 1964, for instance, Louisiana listed candidates’ race on the ballot. Louisiana maintained it was just providing truthful information to the voters of the state. The Supreme Court struck down the statute on the ground that the ballot was not a vehicle to direct voters to consider a candidate’s race.

In the 1990s, Missouri asked congressional candidates to take a term limits pledge; if they refused to do so, the state would indicate on the ballot that the candidate “declined to pledge to support term limits.” The Supreme Court struck down that ballot provision, too.

Both those cases stand for the proposition that states cannot use their ballots to achieve preferred political or policy outcomes — such as burdening those who prefer to keep some, or all, of their tax information private.

UPDATE: Rick Hasen has more on whether states could adopt such measures in Politico.