Trump likely 'inviting' a Republican challenger for 2020 nomination: GOP critic Arizona Sen. Jeff Flake, said Trump will probably face GOP competition in 2020.

 -- President Donald Trump is certain to face competition from an independent candidate if he runs for reelection in 2020 and will probably also be challenged by a Republican for the party's nomination, said Arizona Republican Sen. Jeff Flake, a longtime critic of the president.

"I do believe if the president is running for reelection, if he continues on the path that he’s on, that that’s going to leave a huge swath of voters looking for something else, who are unwilling to go where the president’s going unless he changes course," Flake told ABC News’ Chief White House Correspondent Jonathan Karl on "This Week" Sunday.

"So you’re saying if he is the Republican nominee again, we’re likely to see an independent candidate?" Karl asked.

Flake responded, "Oh yes, I think he’s inviting that. He’s probably inviting a Republican challenge as well ... but certainly an independent challenge."

The Arizona senator, who has announced he is not running for reelection when his term expires in 2018, added that he believes "it is important" for the president to face such a challenge from a conservative.

"I think it is important," Flake said. "People need to see what a traditional conservative looks like ... [and] what it means to believe in the basic tenets of Republicanism", including limited government, economic freedom and free trade.

Flake announced his plans to leave the Senate after polls showed him far behind a challenger endorsed by President Donald Trump’s former senior adviser Steve Bannon.

The Arizona Republican said his opposition to some of the president’s actions would have made a re-election bid tough.

“[R]unning in a Republican primary in Arizona is a daunting task,” the senator said. “There’s a very, very narrow path, unless you’re willing to embrace the president and condone his behavior, and I’m not willing to do that.”