Former Arizona Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE (R) tweeted Monday that President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE was using "authoritarian" language.

"I never thought I would live to see an American President speak this way, using language the can only be described as authoritarian," Flake tweeted, referring to a tweet by Trump in which the president threatened to destroy Turkey's economy if the country does anything "off limits."

"Fellow Republicans, where is the line?" Flake added.

I never thought I would live to see an American President speak this way, using language the can only be described as authoritarian. Fellow Republicans, where is the line? https://t.co/UzYM1ciGnY — Jeff Flake (@JeffFlake) October 7, 2019

Trump's tweet was in defense of his decision to withdraw U.S. troops from Syria while Turkey plans to start a military operation there. Trump also touted his "great and unmatched wisdom." ADVERTISEMENT in defense of his decision to withdraw U.S. troops from Syria while Turkey plans to start a military operation there. Trump also touted his "great and unmatched wisdom."

"If Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will totally destroy and obliterate the Economy of Turkey (I’ve done before!)," he wrote.

"The U.S. has done far more than anyone could have ever expected, including the capture of 100% of the ISIS Caliphate," he added in a subsequent tweet. "It is time now for others in the region, some of great wealth, to protect their own territory. THE USA IS GREAT!"

F lake, a frequent Trump critic, retired from the Senate in January.