Sen. Jeff FlakeJeffrey (Jeff) Lane FlakeFlake donates to Democratic sheriff being challenged by Arpaio in Arizona The Hill's Morning Report - Trump says US-China trade talks to resume, hails potential trade with Japan, UK Joe Arpaio to run for Maricopa County sheriff in 2020  MORE (R-Ariz.) on Tuesday doubled down on his skepticism of Donald TrumpDonald John TrumpTed Cruz knocks New York Times for 'stunning' correction on Kavanaugh report US service member killed in Afghanistan Pro-Trump website edited British reality star's picture to show him wearing Trump hat MORE, saying he currently doesn't believe he'll support the GOP's presumptive presidential nominee in November.

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“As of now, unless he changes significantly, I can’t see myself voting for Donald Trump,” Flake told reporters, according to Bloomberg News, on Tuesday.

The Arizona Republican has been a vocal opponent of Trump, warning that the brash candidate will hurt the Republican Party.

Flake told reporters earlier this year that he would support Ohio Gov. John Kasich over Sen. Ted CruzRafael (Ted) Edward CruzTed Cruz knocks New York Times for 'stunning' correction on Kavanaugh report 2020 Democrats call for Kavanaugh to be impeached Warren: Kavanaugh 'should be impeached' just like Trump MORE (R-Texas) or Trump, as the three battled for the party's nomination.

His latest comments come after he told MSNBC's "Morning Joe" on Monday: Trump wasn't "my first nor my 17th choice" to be the party's nominee.

"It's uncomfortable not having endorsed the Republican nominee, I have to say, but I can't at this point," Flake added. "I hope to be able to support the nominee. I certainly can't right now."

Flake had previously endorsed Sen. Marco RubioMarco Antonio Rubio The 13 Republicans needed to pass gun-control legislation GOP group's ad calls on Graham to push for election security: 'Are you still trying?' Former Massachusetts Gov. Deval Patrick joins CBS News as contributor MORE (R-Fla.), who ended his bid earlier this year.

Republicans have been distancing themselves from Trump's criticism of Judge Gonzalo Curiel, who is overseeing cases against Trump University. The real estate mogul said Curiel won't be fair because of his Hispanic heritage.

Flake on Monday called Trump's comments "very disturbing."

“His statements this week on the judge, that’s a new level,” Flake said on MSNBC. "It’s not just ill-informed or ignorant statements."