Retiring Arizona Republican Sen. Jeff Flake said Sunday that he has "not ruled out" running against President Trump in the 2020 presidential election.

Flake told NBC host Chuck Todd that it's "not in my plans" to run for office, but that he has not yet closed the door on the possibility.

"I do hope that somebody runs on the Republican side other than the president," Flake said.

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Flake said a Republican primary opponent would hopefully remind Trump "what conservatism is" and what his party previously stood for.

In March, Flake also floated the possibility he would face off with Trump in 2020, remarking to a New Hampshire audience that he is a "rare species" in Washington called the "American Conservative -- or Americanus Nevertrumpus."

The Snowflake, Ariz. native said his fellow members of Congress privately have a "lot of alarm" about Trump's actions, especially when it comes to the possibility that the White House could terminate the Mueller probe unilaterally.

"He's obviously probing the edges [of that idea] as far as he can," Flake said, calling Trump's claims of a spy being placed in his campaign a "diversion tactic."

Flake also reacted to Vice President Mike Pence giving a shout out to former Maricopa County, Ariz. Sheriff Joe Arpaio.

Todd said Arpaio is running to replace Flake.

Flake said Pence is a "kind man" and that he is always friendly no matter who he is speaking about.

But, he said Arizonans should be wary of Arpaio over what he said was the sheriff's low level of adherence to the rule of law.

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