Sen. Bob Casey Robert (Bob) Patrick CaseySecond GOP senator to quarantine after exposure to coronavirus GAO report finds brokers offered false info on coverage for pre-existing conditions Catholic group launches .7M campaign against Biden targeting swing-state voters MORE (D-Pa.) is leading his Republican challenger, Rep. Lou Barletta Louis (Lou) James BarlettaBottom Line Ex-GOP congressman to lead group to protect Italian products from tariffs Head of Pennsylvania GOP resigns over alleged explicit texts MORE (Pa.), by 15 points in Pennsylvania's Senate race, according to a Suffolk University poll released Wednesday.

Forty-seven percent respondents surveyed said they are likely to cast their ballots for Casey in November. Thirty-two percent, on the other hand, favored Barletta, while another 21 percent remained undecided.

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Independents also favored Casey by a significant margin, with 31 percent supporting the incumbent and 11 percent saying they are likely to vote for Barletta in November.

Barletta is a staunch backer of Trump. He endorsed the real estate mogul for president relatively early in the 2016 primary season, and was reportedly asked by Trump himself to mount a bid for the Senate.

Casey, on the other hand, has largely opposed Trump's agenda. He voted against the confirmation of Supreme Court Justice Neil Gorsuch last year, as well as the tax cut package championed by the president and congressional Republicans.

Casey's lead in the Suffolk poll is welcome news for Democrats, who are facing a tough Senate re-election map in November. He is among 10 Senate Democrats fending off GOP challenges in states won by President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE in 2016.

The Suffolk University poll surveyed 500 Pennsylvania general election voters from June 21-25. Its margin of error is 4.4 percentage points.