Randy Friese, who is currently a Democratic state representative, told the New York Times he was impressed by Democrat Jon Ossoff running as a nonpartisan candidate.
“Voters need people who have the political courage to stand up for their values and not just bend to the will of the party,” he told the Times.
Friese said he was inspired to get involved in politics after treating Giffords, who was shot in the head in 2011 while attending a constituent event in Tucson. He was elected to the Arizona House in 2014.
According to his website, Giffords and her husband Mark Kelly hosted a campaign event at their home to support Friese in his re-election run last year.
Friese previously served four years in the U.S. Navy Medical Corps.
Flake is considered one of the few potentially vulnerable Republicans in the Senate in 2018 because of his tense relationship with President Donald Trump.
He has already drawn at least one Republican primary challenger.