An attorney who resigned last week as a senior investigator for the House January 6 committee is running for a Missouri US Senate seat as an independent, seeking to stop a far-right former governor, Eric Greitens, who leads the Republican field.

John F Wood, who once worked in the administration of George W Bush, announced that he was beginning the effort to get on the November general election ballot for the seat held by Roy Blunt, a retiring Republican.

Some Republican leaders have expressed concern that Greitens might prevail in a 21-candidate field for the Republican nomination in the 2 August primary, then lose to a Democrat in November because of sex and campaign finance scandals that pushed him from office in 2018.

Greitens also faces allegations of physical abuse from his ex-wife, which he has denied. With the Senate evenly divided, the GOP cannot afford to lose what would otherwise be a safe seat.

Those concerns intensified last week when Facebook removed a Greitens campaign video that shows him brandishing a shotgun and declaring that he is hunting Rinos, or Republicans In Name Only.

“I am conservative and a life-long Republican. But the primaries for both parties have become a race to the bottom,” Wood said.

“This was evident a few days ago when the leading candidate for one of the parties released a campaign advertisement glorifying violence against his political enemies, from his own party no less. Missouri deserves better. Missouri needs another option.”

Wood, 52, was US attorney for Missouri’s western district from 2007 to 2009. He was general counsel for the US Chamber of Commerce when he stepped down in September to become senior investigative counsel for the January 6 committee. He resigned that post on Friday.

A former Republican senator, John Danforth, has urged Wood to run as a right-leaning independent. Wood once worked for Danforth.

Besides Greitens, other Republican contenders include the state attorney general, Eric Schmitt, US representatives Vicky Hartzler and Billy Long, the Missouri Senate president pro tem, Dave Schatz, and a St Louis attorney, Mark McCloskey, who became famous for pointing an assault rifle at protesters for racial equality.

Schatz is positioning himself as a “Reagan Republican”. The others are strong supporters of Donald Trump, who has not yet endorsed a candidate in the race.

Leading Democratic contenders include a former Marine, Lucas Kunce, and Trudy Busch Valentine, who is part of the Busch brewery family.