Former Arizona senator Jeff Flake is leading dozens of 'Republicans against Trump' on the first day of the National Convention in Charlotte.

Flake is among a number of well-known conservative Trump critics to throw their support behind Joe Biden, including Sens. Gordon Humphrey of New Hampshire (now an independent) and John Warner of Virginia.

Last year, Flake wrote a withering indictment of the president in an op-ed which urged fellow Republicans to 'save their souls' and vote for impeachment.

He had, until now, stopped short of endorsing Biden and is expected to make a speech later today on behalf of the 'Republicans for Biden' group.

Fox News reported that he is joined by a raft of former lawmakers, including:

Reps. Steve Bartlett of Texas, Bill Clinger of Pennsylvania, Tom Coleman of Missouri, Charlie Dent of Pennsylvania, Charles Djou of Hawaii, Mickey Edwards of Oklahoma, Wayne Gilchrest of Maryland, Jim Greenwood of Pennsylvania, Bob Inglis of South Carolina, Jim Kolbe of Arizona, Steve Kuykendall of California, Ray LaHood of Illinois (who served as Transportation secretary in the Obama administration), Jim Leach of Iowa, Connie Morella of Maryland, Mike Parker of Mississippi, Jack Quinn of New York, Claudine Schneider of Rhode Island, Chris Shays of Connecticut, Peter Smith of Vermont, Alan Steelman of Texas, Bill Whitehurst of Virginia, Dick Zimmer of New Jersey, and Jim Walsh of New York.