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-Ariz.) on Sunday voiced concerns about President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE's pattern of refusing to criticize Russian President Vladimir Putin ahead of an expected one-on-one meeting between the two leaders next week.

"Many of us are concerned, I certainly am, about the president’s ongoing rhetoric that really demeans or ridicules our allies and praises our adversaries. So this is a part of kind of a continuum, so yes it does concern me," Flake said on CNN's "State of the Union."

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Flake, who is among the most outspoken Republican critics of the president, said he's glad Trump is talking to Putin and negotiating with North Korea.

"But I am concerned, and I know there is concern across Europe, about what might be promised," he added.

GOP Sen. Jeff Flake on President Donald Trump’s upcoming summit with Russian President Vladimir Putin: “I am concerned, and I know there is concern across Europe about what might be promised” pic.twitter.com/9EoykqZblK — CNN Politics (@CNNPolitics) July 8, 2018

Trump is scheduled to meet with Putin on July 16 in Helsinki to cap off a weeklong trip to Europe. He reportedly plans to meet with the Russian president alone, with no aides present, before other officials join the meeting.

While Trump has claimed "nobody is tougher on Russia" than he is, he has drawn frequent bipartisan criticism over his refusal to condemn Putin and Russia for the intelligence community's conclusion that Russia meddled in the 2016 U.S. election.

Trump said he plans to bring up the issue during his upcoming meeting with Putin.

He also suggested last month that Russia should be readmitted to the Group of Seven after it was expelled for annexing Crimea from Ukraine in 2014. The suggestion garnered little traction with other world leaders.

The president revived his friendly rhetoric toward Putin during a rally in Montana last week.

"They’re going ‘Will President Trump be prepared, you know, President Putin is KGB and this and that,’ " Trump told the crowd. "You know what? Putin’s fine. He’s fine. We’re all fine. We’re people. Will I be prepared? Totally prepared. I’ve been preparing for this stuff my whole life."