GOP senator facing reelection won't commit to Trump
© Getty Images

Sen. Pat Toomey (R-Pa.) is raising concerns that he might not be able to support Donald TrumpDonald John TrumpTillerson: Russia already looking to interfere in 2018 midterms Dems pick up deep-red legislative seat in Missouri Speier on Trump's desire for military parade: 'We have a Napoleon in the making' MORE, the latest sign of a growing split over the GOP's presumptive presidential nominee. 

"I've got this set of doubts," Toomey told WAEB, a local radio station, on Monday. "And I hope we don't get to a point where I decide I just can't support him."

Toomey added, "My message to Donald Trump is: You need to unite the Republican Party if you want to win this general election. I hope to get to the point where I can enthusiastically support Donald Trump. I'm not there right now."

Toomey is one of a handful of vulnerable GOP incumbents who are running for reelection in states previously carried by President Obama. GOP Sens. Kelly AyotteKelly Ann AyotteAudit finds US Defense Department wasted hundreds of millions of taxpayer dollars US sends A-10 squadron to Afghanistan for first time in three years No, the US did not spend million on a gas station in Afghanistan MORE (N.H.) Ron JohnsonRonald (Ron) Harold Johnson40 patient advocacy groups oppose 'right to try' drug bill GOP eyes changes to 'right to try' bill Hundreds sign on to letter opposing 'right to try' drug bill MORE (Wis.), Mark KirkMark Steven KirkHigh stakes as Trump heads to Hill Five things to watch for at Trump-Senate GOP meeting Giffords, Scalise highlight party differences on guns MORE (Ill.) and Rob PortmanRobert (Rob) Jones PortmanGOP leader: Congress may settle for pared-down immigration deal Senate Republicans call on Trump to preserve NAFTA Key senator floats new compromise for immigration talks MORE (Ohio) have each said they will support the party's eventual nominee.

His comments come after Trump locked down his status as the party's presumptive nominee last week when rivals Sen. Ted CruzRafael (Ted) Edward CruzSasse statement: Trump nominee who spread conspiracy theories has a ‘tinfoil hat’ Coalition of 44 groups calls for passage of drug pricing bill For the sake of our democracy, politicians must stop bickering MORE (Texas) and Ohio Gov. John Kasich dropped out of the race following Trump's victory in the Indiana primary.

Though Toomey previously suggested he would support Trump if he were the nominee, he's also tried to publicly create space between the two campaigns.

"Trump was not my first, second, or third choice. I object to much in his manner and his policies," he wrote Sunday in a Philadelphia Inquirer op-ed.

Building a wall between the two races is likely an impossible task, with strategists predicting Trump will loom over the Pennsylvania Senate contest. Katie McGinty, Toomey's Democratic opponent, has repeatedly linked the two as she seeks to unseat the GOP senator.

Trump won the state's primary earlier this year but faces an uphill battle in November. A Republican presidential candidate hasn't carried Pennsylvania since 1988.