(CNN) Newly independent Rep. Justin Amash , the only congressional Republican to have publicly argued that President Donald Trump has engaged in impeachable conduct, told CNN that high-level party officials have thanked him behind closed doors for his stance on impeachment proceedings against Trump .

"I get people sending me text messages, people calling me, saying 'thank you for what you're doing,'" Amash told CNN's Jake Tapper in a wide-ranging interview on "State of the Union" Sunday . "They're not saying it publicly. And I think that's a problem for our country, it's a problem for the Republican Party, it's a problem for the Democratic Party when people aren't allowed to speak out."

Amash, who announced Thursday he was leaving the GOP , said that he has had problems with the Republican Party "for several years,"and that he would leave even if Trump were not president. "I don't think there is anyone in there who could change the system," Amash said.

CNN's interview with Amash comes days after he announced in a Washington Post op-ed , "Today, I am declaring my independence and leaving the Republican Party."

"No matter your circumstance, I'm asking you to join me in rejecting the partisan loyalties and rhetoric that divide and dehumanize us. I'm asking you to believe that we can do better than this two-party system -- and to work toward it," he wrote. "If we continue to take America for granted, we will lose it."

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Amash didn't mention the President by name, but his decision to abandon the party comes after months of escalating criticism not just of Trump but of his own colleagues for their failure to hold the President to account, specifically for the actions detailed in special counsel Robert Mueller's report on the 2016 election and its aftermath.

Pelosi's 'making a mistake' on impeachment

In the same interview, Amash said House Speaker Nancy Pelosi should start impeachment proceedings against Trump

"From a principled, moral position, she's making a mistake. From a strategic position, she's making a mistake," Amash said. "If she believes, as I do, that there's impeachable conduct in there, then she should say so. She should tell the American people, we're going to move forward with impeachment hearings and potentially articles of impeachment."

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Amash continued: "When she says things like, 'Oh, I think that we need to have the strongest case before we go forward,' what she's telling the American people is, she doesn't think there's a strong case. If she doesn't think that, then she shouldn't open her mouth in the first place and say she thinks there's impeachable conduct."

On his 2020 plans

The Michigan lawmaker's break with the Republican Party added fuel to growing speculation that he will seek the Libertarian Party nomination and launch a long-shot bid for president in 2020, which he has not ruled out . When asked by Tapper on Sunday about a possible presidential bid, Amash repeated that he "wouldn't rule anything like that out" but said he could not put a timeline on his decision.

Amash was critical Sunday of Trump's impact on the country during his presidency, namely calling out Trump for divisiveness.

"What the President is doing is actually lowering the tone across the country, he's harming civil discourse, he's creating a lot of partisan divide -- he's enhancing it. And I think that's very dangerous for our country and I don't think a lot of people appreciate it," he said.

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Amash also reacted to a recent critical tweet from Trump , where the President called him "one of the dumbest & most disloyal men in Congress." Amash responded, saying, "That's not how people are supposed to talk about each other, to each other."

"(Trump) thinks people owe loyalty to him, but people are elected to Congress with an oath to support and defend the Constitution, not an oath to support and defend one person, the President who happens to be from your own party," Amash said.

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Amash told Tapper that he is still "very confident" that he can win his congressional seat in Michigan as an independent.

"When I go back to my district people are coming up to me and saying, 'Thank you for what you're doing,'" Amash said. "People want open, honest representation. They want people to come to Congress and work with integrity."