President Donald Trump's biggest advantage – the economy – may be his Achilles Heel next year, according to polling by the progressive group Priorities USA.

The survey of five battleground states – Florida, Michigan, Nevada, Pennsylvania and Wisconsin – found that for the first time in Priorities USA's polling, more than half of voters (51%) said Trump's economic policies had not benefited them personally. Another 15% said Trump's economic policies had benefited them "a little" while a combined 34% said his policies helped them a lot or some.

The poll, conducted in August and weighted to represent each state's share of the Electoral College, showed some slippage from May, when Trump did three percentage points better on those metrics. But for Democrats, the 51% number was a critical threshold as they seek to cast Trump as a president who has implemented tax cuts and other policies that help the rich but not the middle class.

"It's the first time we've seen these kind of changes," Guy Cecil, Priorities USA chairman, told reporters in a briefing on the group's strategy to mobilize voters against Trump.

The economy writ large has been doing well, with the stock market generally staying high and the poverty rate recently falling to its lowest level since 2001 . Unemployment is at just 3.7 percent.

Political strategists have long held that incumbents tend to benefit when the economy is going well, and fare poorly when the economy is lagging. Bill Clinton's campaign war room mantra, "It's the Economy, Stupid," helped propel Clinton to victory in 1992 even as the economy under President George H.W. Bush had started to recover.

But what Democrats are banking on is that voters will question whether the "good" economy is in fact helping them. Trump's trade policies, for example, could impact farmers and workers in certain industries, damaging their personal fortune even if the overall impact on the economy is not dramatic.

That has also started to show up in the battleground state polling, Cecil said. For example, 49% of those polled said their incomes were "falling behind" the cost of living, compared to 43 percent who felt that way in May (10% said their income was exceeding the cost of living, compared to 12% who said that in May). That syncs with recent Census Bureau statistics showing median household income was stagnant from 2017-18.

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Further, 35% of those polled in August said their families' financial situations had gotten worse, compared to 25% who reported that in May.

The Priorities USA polling found that health care remains the single most important issue for battleground state voters. Democratic strategists argue that health care, too, is an economic issue because complaints are commonly about the high cost of care.

A separate recent poll by Public Policy Polling of voters in Arizona, Florida, Pennsylvania, Michigan, Wisconsin and Texas, had similar conclusions. Health care is a key issue for 69% of voters in those states, and 68% said they are concerned about people losing their health care coverage if the Affordable Care Act is eradicated. The Trump administration is trying to get the law declared unconstitutional in court.