It’s a politically toxic finding that will provide fodder for critics of the House plan – including those in the Senate, where some Democrats want to limit the benefits of easing the cap to people earning roughly up to $400,000.

“Any SALT relief proposal must prioritize hardworking families that need it most,” said Sen. Bob Menendez (D-N.J.), who has broken with some of his New Jersey colleagues over how far to go in loosening the cap.

“We can do this by limiting the universe of taxpayers eligible for this relief, so that millionaires and billionaires can’t use this as a tax break,” he said.

He and Sen. Bernie Sanders (I-Vt.) are working on an alternative proposal and are expected to have additional details next week.

Menendez's fellow New Jerseyan, Rep. Bill Pascrell (D), scoffed at the Tax Policy Center's analysis.

“I don’t know how many different ways I can say it: the number of middle class New Jerseyans who will benefit from removing the SALT cap is enormous,” Pascrell said in a statement.

“A lot of bad faith actors want to deny my constituents tax relief and I am going to fight back on their propaganda with every breath,” he said.

Democrats have been at odds for months over what to do about the limitation, imposed by Republicans as part of their 2017 tax cuts.

Party leaders are caught between demands from colleagues representing high-tax states, who are threatening to sink their reconciliation plan if SALT isn’t addressed, and others complaining that will only muddle the party’s mantra of soaking the rich.

“The politics is very challenging for Democrats,” said Howard Gleckman, a senior fellow at the Tax Policy Center. “The distributional tables look terrible” for them.

Overall, Democrats’ plan would increase taxes on the well to do while reducing them for average Americans.

Even though most millionaires would receive a tax cut, people with seven-figure incomes — on average — would see their tax bills climb by $68,000, TPC estimates. That’s because one-third of millionaires would face tax increases averaging $228,000.

Aside from easing the SALT cap, Democrats are also proposing new surcharges on the very rich, with those earning more than $10 million facing a new 5 percent surtax. People making more than $25 million would pay another 3 percent on top of that.

So people above those income thresholds would typically pay more under Democrats' plan, even as they benefit from a higher SALT cap, while those making more than $1 million but not enough to face those surcharges would owe less.

Menendez and Sanders are working on a SALT cap proposal that would exempt families making somewhere in the neighborhood of $400,000 – the details are still being tweaked – and finance that by permanently subjecting people making more than that to the $10,000 limit.

That limit is currently set to expire at the end of 2025.