Former Deputy National Security adviser Dina Powell (L) and Steve Bannon exit Marine One on the South Lawn of the White House. File / AFP

As a top adviser to Trump's presidential campaign who later served as chief White House strategist, Bannon helped articulate the right-wing populism and fierce opposition to immigration that have helped define Trump's 3-1/2 years in office. Bannon left the White House in August 2017.

Donald Trump talks to Steve Bannon during a swearing in ceremony for senior staff at the White House. File / Reuters 

Bannon was among several people charged with wire fraud in an indictment by federal prosecutors in Manhattan for allegedly defrauding hundreds of thousands of donors through a $25 million crowdfunding campaign called "We Build the Wall."

Prosecutors said Bannon received more than $1 million of that money through a nonprofit organisation.

Trump's signature effort to build a wall along the US-Mexico border — a key 2016 campaign promise — has struggled amid court challenges, logistical hurdles and opposition from Democrats in Congress.

In the meantime, more than 330,000 supporters have donated to private fund-raisers and profiteers who have promised to build the wall on their own, according to a 2019 Reuters investigation. Those efforts likewise have met with limited success.

The indictment comes as Trump trails in opinion polls behind Democratic challenger Joe Biden ahead of the Nov.3 presidential election.

A spokeswoman for Bannon could not be immediately reached for comment.

Also charged were Brian Kolfage, Andrew Badolato and Timothy Shea.

The donors thought the money would go toward helping to build a border wall, prosecutors said. But Kolfage, whom they described as the public face and founder of the operation, received thousands of dollars that he used to fund a lavish lifestyle.

Kolfage is due to appear in federal court later on Thursday in Florida, while Bannon is set to appear in federal court in Manhattan. The other two defendants are due to appear in courts in the Middle District of Florida and Colorado.

Reuters