Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeRepublican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style Bush endorsing Biden? Don't hold your breath MORE (R-Ariz.) in an interview broadcast Sunday said he wished the Republican Party had stood up to birtherism.

On NBC’s “Meet the Press,” host Chuck Todd discussed Flake’s new book about conservatism and asked the Arizona senator if the GOP is afraid to put country over party.

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“Well, I do think that we've seen more people ready to stand up. And I wish that we, as a party, would have stood up, for example, when the birtherism thing was going along. A lot of people did stand up but not enough,” Flake told Todd.

Flake said the birther movement, a conspiracy theory that claimed former President Barack Obama Barack Hussein ObamaObama calls on Senate not to fill Ginsburg's vacancy until after election Senate Republicans face tough decision on replacing Ginsburg Cruz: Trump should nominate a Supreme Court justice next week MORE was not born in the United States, “was particularly ugly.”

President Trump had promoted the theory for years, before rejecting it during the 2016 presidential campaign.

"President Barack Obama was born in the United States," Trump said at the end of a campaign event last September. "Period."

Flake on Sunday also denounced the “lock her up” chants about Democratic presidential candidate Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE, which could be heard at Trump rallies during the 2016 election

The Arizona lawmaker, who has not shied away from criticizing Trump and his own party, has been completing a media blitz promoting his new book, “Conscience of a Conservative.” He has argued that the GOP is in denial about the first few months of Trump’s presidency.