Democrats in Springfield are trying to keep President Donald Trump off the Illinois ballot in 2020 unless he agrees to release his income tax returns, which he refused to do during his 2016 campaign.

The measure is expected to be voted on as early as this week in the state Senate, where Democrats maintain a big majority over Republicans.

The push is similar to efforts in 17 other states, where Democrats have filed nearly identical legislation this year to erect an electoral roadblock to Trump’s re-election.

The U.S. Constitution spells out simple requirements for president: A candidate must be a natural-born American citizen, at least 35 years old and have been a resident of the U.S. for at least 14 years.

But state Sen. Tony Munoz, D-Chicago, wants to add a requirement that would force presidential candidates in Illinois also to submit their previous five years’ worth of income tax returns in order to qualify for the statewide ballot in 2020 and beyond.

“It’s not about party. Everybody would have to do it. It’s not like I’m just going after independents [or] Republicans,” Munoz, a member of Senate President John Cullerton’s leadership team, told WBEZ in an interview.

“This will show the voters … transparency of how [a candidate] made their money and make sure there is no potential conflict in the future if he or she becomes president or vice president of the United States,” Munoz said.

Since February, Democratic-led legislative chambers in Washington state, Hawaii and New Jersey have passed similar measures, raising constitutional questions about how far individual states can go in mandating qualifications for president.

In Illinois, the head of the state Republican Party says Munoz’s push is simply aimed at Trump. Chairman Tim Schneider says the bill poses a double-standard since personal financial information isn’t required of others appearing on the ballot, including long-serving Democratic House Speaker Michael Madigan, of Chicago.

“I think this is very politically motivated and hypocritical,” Schneider said. “This is driven by Democratic-led legislatures, no Republican legislatures. I don’t think you’ll see Republican support unless the Democrats are held by these same rules and accountability as Republicans.”

Democrats control 40 seats in the Illinois Senate compared to 19 seats held by Republicans. Munoz needs 30 votes to pass his legislation to the House, and he said he believes he has that number locked up.

“We’ll definitely have the Democrats on our side of the aisle,” Munoz said.

Not everyone in Democratic politics, however, thinks the idea is good – or even legal.

Michael Dorf is a veteran Chicago election lawyer who once represented former President Barack Obama during his bid for Congress and the U.S. Senate. Dorf, who also has done work for the Democratic Party of Illinois, believes the legislative demand for presidential tax returns could be knocked down by the courts.

“I’ve done this for over 25 years, and I’ve only represented Democrats and progressives. And I would love to see him to have to finally disclose those returns,” Dorf said of Trump. “But I just don’t think it’s constitutional.”

“The requirements for president are built into the U.S. Constitution, and a state can’t add additional requirements,” Dorf said. “They couldn’t require a president to be 37 years [old] instead of 35. They couldn’t require a candidate for president to have lived in Illinois.”

If the bill passes the Senate, its prospects in the House appear good, considering Democrats hold a supermajority over Republicans there, as well.

Gov. Pritzker hasn’t taken a public stance on the legislation. A spokeswoman would only say the legislation is under review when asked whether Munoz’s measure had the governor’s support and whether he’d sign it if it reached his desk.

If the plan got enacted later this year, it would only add to Trump’s political problems in Illinois.

The president lost the state in 2016 to Democrat Hillary Clinton by 17 percentage points. His standing here hasn’t improved much since then, according to a poll released last week by Southern Illinois University’s Paul Simon Public Policy Institute.

Only 39 percent of Illinoisans surveyed by the organization in mid-March gave Trump favorable job performance marks, compared to 59 percent who held a negative view of his work in the White House.

Dave McKinney covers Illinois politics and government for WBEZ. Follow him @davemckinney.