Senior officials at the Department of Homeland Security (DHS) interpreted the order to mean that lawful permanent residents - green card holders – who hailed from the seven Muslim-majority countries targeted in the immigration order would not face additional screening when they entered the country.
But they were quickly overruled by Bannon, who is Trump’s chief strategist and oversaw the drafting of the executive order along with White House senior policy adviser Stephen Miller, a close ally of Bannon's, the officials said.
"They were in charge of this operation," one senior DHS official said, adding that the experts were "almost immediately overruled by the White House, which means by Bannon and Miller."
A senior national security official described the pair as a "tag team" pushing Trump's key policies, including the immigration order which bars the entry of refugees and places a temporary hold on people from seven countries - Syria, Yemen, Iraq, Iran, Sudan, Somalia and Libya.
The inclusion of green card holders from those countries intensified opposition to an executive order that sparked legal challenges, protests at airports and sharp criticism from inside the Republican Party, including from some Trump allies.
DHS officials say there was little or no White House consultation with immigration, customs and border security agencies on the immigration policy change, causing widespread confusion over how to implement Trump's order.
A senior administration official said the order went through a review by "key people" at DHS and the White House National Security Council, and that several immigration staff on Capitol Hill were involved in drafting the order.
But officials said Bannon was the driving force throughout.
The White House declined to comment on his role.
Critics have accused Bannon of harboring anti-Semitic and white nationalist sentiments. Under Bannon's leadership, his Breitbart website presented a number of conspiracy theories about Trump's Democratic rival in the 2016 election, Hillary Clinton, as well as Republicans deemed to be lacking in conservative bona fides.
Bannon has ascribed his interest in populism and American nationalism to a desire to curb what he views as the corrosive effects of globalization. He has rejected what he called the "ethno-nationalist" tendencies of some in the movement.
After becoming chief executive of Trump's election campaign in August, the former Goldman Sachs banker and Navy veteran helped lead him to victory over Clinton. He was then appointed by Trump as senior counselor and chief strategist - jobs not subject to U.S. Senate confirmation.
He has been an almost constant presence by Trump's side in the first 10 days of the administration - in the White House for a meeting with American manufacturers, at CIA headquarters the day after Trump was sworn in, and in the Oval Office during British Prime Minister Theresa May's visit.
He appears to have greatly expanded his power in the first 10 days of Trump's presidency.
ELEVATION TO NSC
Trump gave him an unprecedented seat in the NSC's top-level meetings and potentially narrowed the role played by the director of national intelligence (DNI) and the chairman of the Joint Chiefs of Staff.
Bannon has also asserted authority over almost all written statements from the White House and the NSC and has sent back documents for rewrites as he sees fit, one NSC official said, speaking on condition of anonymity.
Critics, including four senior U.S. intelligence officers, called the decision to formalize Bannon's role at the NSC meetings a mistake, saying it risks politicizing decisions on national security.
White House spokesman Sean Spicer on Monday defended Bannon's inclusion in the NSC.
Susan Rice, the former national security adviser in former President Barack Obama's administration, tweeted on Sunday: "This is stone cold crazy. After a week of crazy."
Bannon and Miller are drowning out the opinions of more moderate advisers like White House Chief of Staff Reince Priebus, said a senior DHS official and two people in Washington who work closely with the White House on immigration and a range of other issues.
One of those people and the DHS official said Priebus felt he had placed enough of his fellow moderate Republicans in key positions at the White House as a counterbalance to Bannon and Miller, but he has been frustrated at their outsized influence so far, especially on issues of immigration and national security.
The White House dismissed the views of the officials as gossip.
Banner and thumbnail credit: Reuters