There are many Republicans, mostly not presently in public office, who have made it clear they are not supporting Donald Trump for reelection, and some going further and endorsing Joe Biden.
Among those making clear they will not back Trump are the following:
Former President George W. Bush
Former Florida Governor Jeb Bush
Senator Mitt Romney of Utah
Former National Security Adviser John Bolton
Former Senator Jeff Flake of Arizona
Retired Four Star Navy Admiral William McRaven (who directed the raid that killed Osama bin Laden in 2011)
Among those expressing doubt but not yet committing are the following:
Former Speaker of the House John Boehner of Ohio
Former Speaker of the House Paul Ryan of Wisconsin
Former White House Chief of Staff and General John Kelly
Senator Lisa Murkowski of Alaska
Former Congressman and Governor Mark Sanford of South Carolina
Former Director of National Intelligence and Senator Dan Coats of Indiana
Among those formally endorsing and supporting Joe Biden are the following:
Former Governor and Congressman John Kasich of Ohio
Former New York City Mayor Michael Bloomberg
Former New Jersey Governor Christie Todd Whitman
Former California gubernatorial nominee Meg Whitman of California
Former Secretary of Defense and Nebraska Senator Chuck Hagel
Former Secretary of Defense and Marine Corps General James Mattis
Cindy McCain, wife of former Senator John McCain
Former Presidential contender in 2016 Carly Fiorina
Former Congresswoman Susan Molinari of New York
Former Secretary of State Colin Powell
Former Department of Homeland Security Chief of Staff Miles Taylor
Retiring Florida Congressman Francis Rooney
Conservative commentator George Will
Conservative commentator Bill Kristol
Republican strategist Steve Schmidt
Republican strategists Rick Wilson
Republican strategist John Weaver
Republican strategist George Conway, husband of Trump advisor KellyAnne Conway
Also, a number of Republican groups opposed to Trump are spending tens of millions on advertising to oppose Trump, including
The Lincoln Project
Republican Voters Against Trump
43 Alumni For Joe Biden PAC (referring to George W. Bush)
Republicans For The Rule Of Law