(CNN) - As President Donald Trump continues to resist requests for his tax returns from Democrats in Washington, state lawmakers are moving to require him to release his financial information if he wants to run for president again in 2020.
Lawmakers in 18 states across the country, including New York, Illinois and Washington, have introduced bills that would require all presidential candidates and their running mates to release their individual tax returns in order to qualify for the presidential primary ballot, according to the National Conference of State Legislatures.
The latest is in Illinois, where state senators approved a bill this month that would require presidential candidates and their running mates to release personal tax returns for at least the five most recent years in exchange for access to the state's 2020 ballot. It's unclear whether the measure will succeed in the Illinois House or if the state's Democratic Gov. J.B. Pritzker would sign the bill if it passes.
Trump is the only President in modern history who's refused to voluntarily release his tax returns, and also to maintain his interest in his personal business while in office, prompting questions and lawsuits about potential conflicts. Several Democratic 2020 candidates have already released their tax information, seeking to draw a contrast with Trump.
On Tuesday, the Trump administration again blew past a deadline from House Democrats for six years of Trump's tax returns, which they have requested under an obscure anti-corruption statute. Instead, Treasury Secretary Steven Mnuchin wrote he would respond to House Ways and Means Committee Chairman Richard Neal's request by May 6, after the Justice Department concludes its legal review.
The tax return bills, however, would sidestep that fight -- though it isn't clear if the risk of missing the ballot on states likely to give their Electoral College votes to a Democrat in 2020 would sway Trump.
And it remains an open question whether states requiring presidential candidates to release their tax returns to get ballot access would be constitutional.
Dylan Lynch, a policy associate for the National Conference of State Legislators, wrote in a recent blog post that although states have the authority to administer presidential elections, it is the Constitution that clearly outlines the qualifications for the presidency. The criteria include being a natural-born citizen, at least 35 years old and a resident of the US for the past 14 years.
"The possible addition of a new criteria established by a state would surely face court battle," Lynch wrote.
The Supreme Court has previously ruled that neither states nor the federal government can create additional qualifications for members of Congress, and some legal experts believe that would likely extend to the President of the United States.
With a few exceptions, nearly all of the state bills that have been introduced would require candidates to release at least five years of individual tax returns. In Mississippi, Democratic state lawmakers failed to win the release of the candidate's tax returns for only the year prior to the primary, while a bill introduced in North Carolina would require at least 10 years of personal tax returns.
House Democrats are also seeking to revise the law to require tax return disclosure after seizing control of the chamber during the 2018 midterm election.
Under a wide-ranging election reform bill that passed along party lines in the House last month, presidents would be required to disclose 10 years of tax returns to the Federal Election Commission. It's unlikely the Republican-controlled Senate will follow suit, or that Trump would sign such legislation.
Earlier this month, Democratic lawmakers in New York also initiated a separate push to authorize the state's tax commissioner to release state tax returns to Congress upon request. Those returns could be as revealing as federal returns given that Trump is a New York resident and the state is home to the headquarters of his family business, the Trump Organization.
Previous efforts to require transparency have failed.
Former Republican New Jersey Gov. Chris Christie called it a "transparent political stunt" when he vetoed such a bill last year. Even California Democratic Gov. Jerry Brown vetoed a bill in 2017, when he said the measure sets a "slippery slope" of what individual states could require of candidates in the future.
"Today we require tax returns, but what would be next?" said Brown at the time. "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?"
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