Republican presidential nominee Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE lashed out at Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R-Ariz.) Sunday on Twitter.

He tweeted that the Republican Party needs “strong and committed leaders, not weak people such as @JeffFlake” in order to address illegal immigration.

The Republican Party needs strong and committed leaders, not weak people such as @JeffFlake, if it is going to stop illegal immigration. — Donald J. Trump (@realDonaldTrump) September 4, 2016

The Great State of Arizona, where I just had a massive rally (amazing people), has a very weak and ineffective Senator, Jeff Flake. Sad! — Donald J. Trump (@realDonaldTrump) September 4, 2016

Earlier Sunday, Flake reiterated on CNN’s “State of the Union” that he would not be voting for Trump in November.

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“I just know that I would like to vote for Donald Trump. It’s not comfortable to not support your nominee. But given the positions that he’s taken and the tone and tenor of his campaign, I simply can’t.”

Flake also said that if there was any “softening” from Trump on undocumented immigrants, “it was buried pretty deep.”

Trump last week laid out a 10-point hard-line immigration plan during a speech in Phoenix, Ariz., in which he vowed to build a wall on the nation's southern border and warned that no one in the country illegally would be exempt from deportation.

He had previously called for the immediate deportation of the roughly 11 million people living in the country illegally.