The former president refused to throw his support behind Mr Bush, the only member of his famous family to support Mr Trump after the rest snubbed his inauguration and both of his Republican nomination conventions.
This was made more striking because the Bush family had the only two living Republican ex-presidents during Mr Trump’s single term in office.
“Attorney General Ken Paxton has been bravely on the front line in the fight for Texas, and America, against the vicious and very dangerous Radical Left Democrats, and the foolish and unsuspecting RINOs that are destroying our Country,” said Mr Trump ion a statement that failed to mention Mr Bush.
Mr Bush is the son of former Florida Governor Jeb Bush, who Mr Trump mocked as “low energy” during the 2016 Republican presidential primary.
He is also the state’s Land Commissioner and met with Mr Trump at his gold course in Bedminster, New Jersey, earlier this month.
Mr Paxton has been a vocal supporter of Mr Trump, and filed a lawsuit in 2020 that challenged the former president’s election defeat in four battleground state.
The US Supreme Court declined to hear the case, but Mr Paxton went on to speak at Mr Trump’s rally on 6 January before the Capitol riot.
Following Mr Trump’s endorsement of Mr Paxton, Mr Bush took to Twitter to highlight the legal issues that his election opponent faces.
Mr Paxton has been under securities fraud investigation for a large portion of his time in office, and has also faced an FBI investigation into wether he abused his position by helping a wealthy donor.
He has denied any wrongdoing in both cases.
“I’m running for Attorney General because Texans deserve integrity and honesty from the office of Texas’ top law enforcement official,” said Mr Bush.
“Texans deserve a candidate without a laundry list of existing and potential criminal indictments.”