A group of former staffers to Mr Bush have set up a political action committee, named 43 Alumni for Biden, in reference to him being the 43rd US president.
The group is comprised of prominent former and current Republicans, who are campaigning to stop Mr Trump winning reelection, and has regularly released videos over the past couple of months, attacking his leadership.
Jennifer Millikin, who is one of the organisers of 43 Alumni, as well as a former staffer on Mr Bush’s 2004 reelection campaign, said that although many members disagree with Mr Biden’s policies, they believe they must oppose the president.
“We know what is normal and what is abnormal, and what we are seeing is highly abnormal. The president is a danger,” Ms Millikin said.
Reuters also spoke to two other former officials who are members of the group, Karen Kirksey and Kristopher Purcell, who worked as a communication official and on the former president’s 2000 election campaign respectively.
“This November, we are choosing country over party,” Mr Purcell said. “We believe that a Biden administration will adhere to the rule of law...and restore dignity and integrity to the White House,” he added.
“We really have had overwhelming support for our efforts,” Ms Kirksey told the agency.
The campaign group is not ready to release the names of all its donors, but will have to submit them to the Federal Election Commission by October.
Mr Bush has been vocal in the last couple of months, and called the death of unarmed black man George Floyd a “shocking failure” and released a video calling for unity during the coronavirus pandemic.
However, Freddy Ford, who is Mr Bush’s spokesman, told Reuters that he has retired and “and won’t be wading into this election.”
Erin Perrine, director of press communications for the Trump campaign told the Independent: ”This is the swamp — yet again — trying to take down the duly elected President of the United States.
“President Trump is the leader of a united Republican Party where he has earned 94% of Republican votes during the primaries — something any former president of any party could only dream of.”