Democratic presidential front-runner Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE leads likely general election rival Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE by 7 points in a new poll of middle-income voters in the Rust Belt states of Michigan, Ohio, Pennsylvania and Wisconsin.

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Clinton leads Trump, 46 percent to 39 percent, in a Purple Slice online poll of voters with annual family incomes between $30,000 and $75,000 for Bloomberg Politics released Thursday morning.

Pollster Doug Usher said Trump “may need to build a more conventional Republican coalition to win” if he can’t improve his standing among working-class voters, Bloomberg reported.

Wednesday's results also show that middle-income Rust Belt voters believe Clinton has the edge in temperament and foreign policy. Forty-nine percent say the former secretary of State has "the right temperament" for the presidency, versus 22 percent who said the same thing about for Trump.

Fifty four percent, meanwhile, believe Clinton has "the skills needed" for conducting foreign policy, compared with Trump's 22 percent.

Neither White House hopeful is popular with Rust Belt voters, however.

Sixty-four percent view Trump unfavorably, while 56 percent say the same of Clinton.

Nearly half — 45 percent — say they would consider a third-party candidate if Clinton and Trump are their choices in November.

The results additionally show that few voters trust either Clinton or Trump.

Twenty-nine percent say Clinton is more trustworthy, compared with 23 percent who pick the billionaire instead. Forty-eight percent are not sure who should be trusted more.

The survey of 803 respondents, conducted May 18-24, has a margin of error of 3.5 percentage points.

—This report was updated at 8:10 a.m.