WASHINGTON – More than two years before the 2020 presidential election, Republican Sen. Jeff Flake, who has been a vocal Trump administration critic and is retiring at the end of the year, has a message for Republicans: not Donald Trump, no matter the cost.

Speaking at the National Press Club on Thursday, Flake rebuked the president for what he sees as “the degradation” of American values under Trump’s leadership. While he said that running for president is not in his plans, he hopes that a fellow conservative will challenge Trump in the Republican primaries.

“Republicans want to be reminded, I think, of what conservatism really means,” Flake said, citing free trade and immigration as key issues. “If one voice can do such profound damage to our values and our civic life, then one voice can also repair the damage.”

But anti-Trumpers may face an uphill battle if they choose to oppose the president in 2020, experts suggest.

“It’s very unusual for a president to be primary challenged,” said Samuel J. Abrams, a visiting scholar at the conservative American Enterprise Institute, in an interview. In recent political memory, three presidents ran against members of their own party – President Gerald Ford was challenged by Ronald Reagan in 1976, Ted Kennedy ran against President Jimmy Carter in 1980 and Pat Buchanan took on President George H.W. Bush in 1992 – and each president emerged from the primary victorious. However, all three ultimately failed to win their general elections.

Presidential Primary Challenges by Libby Berry

Running against Trump would be a calculated risk, Abrams said, and one that not every presidential hopeful would be willing to make. In an interview with CNN’s Jake Tapper on Wednesday, Flake mentioned Ohio Gov. John Kasich, Trump’s last remaining challenger in the 2016 Republican primaries, and Nebraska Sen. Ben Sasse as possible candidates, but neither have said they would enter the race. Someone like Sasse may want to run for president in the future, Abrams said, and a primary battle with Trump might leave him weak if his gamble didn’t pay off.

Even so, Republicans “might not deserve to lead” if they can’t stand up to the president, Flake said. “This is not a time for pretending.”

If someone does run against Trump, the candidate will need to differentiate himself or herself from the Trump machine and return to party roots to have any chance of success, Abrams said.

“It has to be a Republican who understands traditional conservative values, but also has their finger on the pulse of where the country is going,” he said.

Following the school shooting in Parkland, Florida, the national conversation around gun safety is changing, he said, and potential candidates will have to react and respond accordingly. He noted that many Republican members of Congress have already criticized Trump’s decision to impose steel and aluminum tariffs, and that the door is open for more Republicans to speak out ahead of 2020.

Still, Flake pointed to “amnesia” from within the party when it comes to Trump as a real concern, adding that the president remains popular among those who vote in Republican primaries. Touching on his own decision to leave the Senate, Flake said he did not believe he could win his Arizona primary in the current political climate.

“Make no mistake, the Republican Party right now is President Trump’s party,” Flake said. “It would be a tough challenge for anyone to take, and I just hope someone does it.”