Charles Flores wants to use Texas’s “junk science” law to appeal his conviction.
The former president will tour the border with Abbott, who has promised to build a state-funded border wall.
After a string of legal defeats, President Trump said his team may step in to support Attorney General Ken Paxton's challenge.
Bush, who also served as Texas governor, called Biden "a good man, who has won his opportunity to lead and unify our country."
Ramos, an unarmed Black and Latino man, was killed as he pulled out of a parking spot after officers shot him with "less-lethal" munition.
