The survey , conducted by the public affairs firm Firehouse Strategies and data analytics firm 0ptimus, also found Trump's approval rating underwater in Michigan, Pennsylvania and Wisconsin — three states he won by a collective 77,000 votes in 2016, giving him enough electoral votes to clinch the White House.

ADVERTISEMENT Just 42 percent of Wisconsin voters surveyed approve of Trump's job performance, and only 43 percent of Pennsylvania voters feel the same, according to the poll. Trump's approval ratings have dropped by 2 points and 3 points in those states, respectively.

In Michigan, 45 percent of voters approve of the job Trump is doing, while 49 percent disapprove. That rating is virtually identical to the last time Firehouse and 0ptimus surveyed those states , in June.

But the poll found Trump running virtually even with, or only slightly behind, the three leading Democratic candidates.

In Pennsylvania, Biden posts the best numbers among potential Trump rivals. The former vice president leads Trump 45 percent to 41 percent. Sanders leads the president 44 percent to 42 percent, while Warren holds a 43 percent to 41 percent lead — both well within the poll's margin of error of plus or minus 4.2 percentage points.

Michigan is the only state where Trump holds a lead over any Democratic candidates, though that is also within the survey's margin of error.

Trump leads Sanders 43 percent to 40 percent in the state, and holds a 1 point lead over both Warren and Biden — 42 percent to 41 percent and 42 percent to 41 percent, respectively.

Trump's low approval ratings make him vulnerable in 2020, in part because those ratings are soft, the pollsters said. In all three states, at least 10 percent of respondents only somewhat approve of his performance.

"In each state, the proportion of strong opinions is dominated by strong disapprovers," the pollsters wrote. "This seems to indicate that he has much more room to fall than to rise in these states."

The polls show little change since the last Firehouse/0ptimus survey in June, though Trump's standing has dropped notably in Pennsylvania.

Trump won 306 electoral votes in the 2016 presidential contest, 46 of which came from the three Midwestern battleground states. He can afford to lose two of the three and still carry the White House, assuming Democrats do not make inroads in any other states around the country. But without winning at least one of the three states, Trump's path to a second term virtually disappears.

The Firehouse/0ptimus survey, conducted Saturday through Monday, interviewed 1,590 likely general election voters across the three states — 534 in Wisconsin, 529 in Michigan and 527 in Pennsylvania. The polls carry margins of error of 4 percent to 4.2 percent per state.