CAMP HILL, Pa. -- Republican U.S. Sen. Pat Toomey, in a neck-and-neck race to keep his seat in the presidential battleground of Pennsylvania, said Friday he expects Democrat Hillary Clinton will face congressional investigations next year if she becomes president.

However, Toomey didn't go as far as some Republican congressional colleagues in saying Clinton should face impeachment proceedings.

"I'm sure there'll be investigations," Toomey said after touring a plumbing supply warehouse in suburban Harrisburg as part of his pitch as a champion of small businesses. "She absolutely and definitely jeopardized American's security, knowingly, by running her own private email server because she had to keep her emails secret."

But, he said, grounds for impeachment involve constitutional and legal questions he hadn't looked into and couldn't answer.

Still, Toomey said it appeared Clinton had received special treatment from the Department of Justice in avoiding charges related to her use of a private email server while secretary of state.

Toomey was travelling the state Friday and used the opportunity to chide his Democratic challenger, Katie McGinty, as "holed up" and avoiding reporters.

McGinty appeared Friday at a Pittsburgh rally with Clinton and was scheduled to appear Saturday with Vice-President Joe Biden in suburban Philadelphia.

The election is Tuesday.

Toomey, who compiled one of Congress' most conservative voting records, is among the Senate's most endangered incumbents and has run at arm's length from Republican presidential nominee Donald Trump in a state that leans Democratic.

McGinty, who served in Bill Clinton's White House and was recruited to run by national Democrats, has stayed quiet about Hillary Clinton's controversies while piggybacking on rallies headlined by high-profile Democrats visiting Pennsylvania.

The race could help determine control of the Senate as the GOP struggles to hold its 54-46 majority. The state's two largest newspapers have split on the candidates, with The Philadelphia Inquirer endorsing McGinty and the Pittsburgh Post-Gazette endorsing Toomey.

With reported spending on the race since the start of 2015 surpassing $155 million, the nonpartisan government transparency think-tank the Sunlight Foundation said the election appears to be the most expensive U.S. Senate race ever.

McGinty, speaking before Clinton at a banquet hall at Heinz Field, hammered Toomey over his middle-of-the-road stance on Trump, refusing to endorse him but refusing to disavow him. Toomey also hasn't said for whom he'll vote on the presidential ballot.

Toomey, McGinty suggested, hadn't stood up to Trump.

"In politics, the definition of courage and character is doing the right thing, even though it might cost you some votes," McGinty said, according to a campaign transcript. "Pat Toomey has failed the test of courage and character."

Toomey has sought to use McGinty's closeness to Clinton to his advantage, highlighting his criticism of Trump over Trump's vulgarity and immigration plans as proof of his independence.

Creating space between himself and Trump could be crucial to winning moderates and independents from whom he'll likely need strong support in a state where registered Democrats outnumber Republicans by a 4-3 ratio. But Toomey also risks alienating Republican voters who delivered a 37 percentage-point victory for Trump in Pennsylvania's April 26 primary.