Washington( CNN) Controversial former Sheriff Joe Arpaio on Wednesday called former President Barack Obama’s birth certificate a “phony document” in an interview on CNN.

Arpaio announced Tuesday that he is running for the Arizona US Senate seat currently resided by Sen. Jeff Flake, who is retiring from Congress at the end of his term.

He was a staunch supporter of President Donald Trump during the campaign, and was pardoned by the President in August. The former Maricopa County sheriff was convicted for defying a court order to stop racially profiling Latinos, and he has been widely criticized for his hard-line stances on immigration.