President Trump stormed into the White House thanks, in part, to working-class voters. Well, that was the conventional wisdom, in any case (there’s some debate over how big a factor economic anxiety actually was). But whatever working-class support Trump has, the Republican push to overhaul U.S. health care is putting it in peril.

The American Health Care Act, which may come up for a vote in the House this week (or not), appears to divide the Republican base along income lines. More specifically, Trump’s backing of the AHCA — and the renewed GOP effort to pass the bill — could eat away at the president’s support among lower-income Americans who otherwise like the job Trump is doing.

In early April, FiveThirtyEight teamed up with SurveyMonkey to poll 7,000 Americans about their feelings on Trump. Among other questions, SurveyMonkey asked people whether they approved of the job Trump was doing as president and whether they approved of how Trump was handling health care. A large majority (80 percent) of respondents who approved of the job Trump was doing also approved of the job he was doing on health care. That shouldn’t be too surprising — generally, people who support a president support him on most issues. (Otherwise, they wouldn’t support him overall.)

But among people who approved of Trump, support for what he was doing on health care was weakest among lower-income respondents.

FAMILY INCOME TRUMP APPROVAL ON HEALTH CARE Less than $15,000 65% – Between $15,000 and $29,999 73 – Between $30,000 and $49,999 76 – Between $50,000 and $74,999 82 – Between $75,000 and $99,999 86 – Between $100,000 and $150,000 83 – More than $150,000 88 – Lower-income Trump supporters are less likely to approve of how he’s handling health care Survey conducted March 31 through April 7 Source: SurveyMonkey

Just 65 percent of Trump supporters who are part of families making less than $15,000 a year liked the way he was handling health care. From there, health care approval climbs pretty consistently — jump up an income bracket and support for Trump on health care jumps, too. Indeed, among Trump supporters, the correlation between a respondent’s income and whether they approve of how Trump is handling health care is +0.94. When you go to the top of the income chain (those people whose household income is over $150,000), support for Trump on health care jumps to 88 percent — 23 percentage points higher than among the lowest income bracket.

A big chunk of Trump’s base — 37 percent — are in the bottom three income brackets in the table above (part of households that make less that $50,000 per year), according to the SurveyMonkey poll. The White House might decide it’s worth pushing past their reticence on health care reform in order to get a legislative win (in the House, at least). But we’re not talking about a trivial part of Trump’s coalition.

This doesn’t seem like some statistical fluke in the survey data, either. Prior polling on health care from the Pew Research Center showed Republicans whose families make less than $30,000 a year were nearly three times more likely than those in families making at least $75,000 to say it was the government’s responsibility ensure Americans had health care coverage. And the large divide along income lines in the AHCA polling makes sense given who would do better under the plan versus under the current system (the Affordable Care Act).

The ACA provides tax credits for people to buy health insurance based on how much money they make. But, according to a Kaiser Family Foundation analysis, individuals making less than $20,000 would see those credits cut more than any other group under the AHCA. Health care would become a lot more expensive for them. Some individuals making less than $20,000 could see their tax credit decrease by over $8,000, or 40 percent or more of their income. (The exact change in cost would depend on where they live, how old they are, or how sick they are.) Meanwhile, some families making over $100,000 per year could gain tax credits they don’t get from the ACA.

Many of Trump’s voters, in other words, would have the most to lose under the Republican’s health care bill. And that shows up in the polling data. In the SurveyMonkey poll, 22 percent of people who approve of Trump but disapprove on health care rate it as the most important issue right now. Just 15 percent of people who approve of Trump and the job he is doing on health care rank health care as their top issue. To put it another way, health care was ranked as the second-most important issue by Trump supporters who disapprove of the job he is doing on health care, while it ranked as the fourth-most important for Trump supporters who specifically support his health care push.

It’s a precarious situation for Trump. We’ve already seen Americans, including Republicans, sour on Trump because of health care. In the week after the House’s initial push to pass the AHCA fell apart in March, Trump’s approval rating dropped below 40 percent for the only time in his presidency, according to FiveThirtyEight’s approval tracker. (According to Gallup, it was also at this time that his approval dropped to its lowest level among people, including Republicans, making less than $60,000 a year.) Since then, his approval rating has recovered to 42 percent.

Republicans tried this before and got burned. Trying it again with an even more conservative bill seems likely to have the same result.