"It's not only not going to get better it's going get worse," Bannon told thousands of grass roots activists attending the Conservative Political Action Conference (CPAC) just outside Washington, referring to media organisations who he said were "opposed to the economic nationalist agenda" laid out by the new president.
"If you think they're going to give the country back without a fight, you are sadly mistaken," Bannon said in one of his first public speeches since the January inauguration.
"Every day, every day is going to be a fight."
Bannon, the former chief of Breitbart, a popular conservative website that has faced criticism for fuelling the so-called "alt-right" movement that includes racist, anti-Semitic and anti-immigrant elements, is among the most provocative members of Trump's inner circle.
He is seen as wielding immense power with the president, who has come to lean heavily on the former Goldman Sachs executive for the direction of his economic and foreign policy agenda.
In his attacks on the American press, Trump has an ally in Bannon, who described the media as "the opposition party" that "betrayed the campaign, and is now betraying the administration."
Bannon was joined on stage by White House chief of staff Reince Priebus, who proclaimed Trump the uniter of the movement through his shock election victory in November.
"The truth of the matter is ... Trump brought together the party and the conservative movement," Priebus said.
"And I've got to tell you, if the party and the conservative movement are together, similar to Steve and I, it can't be stopped."
Bannon and Priebus have reportedly been at odds, amid rumors of internal White House rivalries. But at CPAC, Priebus played down any discord between them.
The two share an office suite, and work together for some 17 hours a day, Priebus was quick to point out.
But even in the banter, Bannon appeared to inadvertently highlight their differences.
"I have a little thing called the war room, he has a fireplace, nice sofas," Bannon said.
Bannon appeals to conservatives
Donald Trump's chief strategist Steve Bannon has appealed to conservatives to unite behind the Republican president as he presses his agenda.
Bannon took to the stage along with White House chief of staff Reince Priebus at the four-day Conservative Political Action Conference, telling the gathering, "We want you to have our back" in upcoming battles, and denouncing media criticism of Trump.
The early days of the administration have been marked by deep post-election divisions between Trump backers and liberals over the new president's travel ban on refugees and people from seven Muslim-majority countries, as well as moves to increase deportations of illegal immigrants and to build a wall on the border with Mexico.
While conservatives are celebrating Trump's role in delivering them a victory in November's election, his agenda veers from traditional right-wing principles like limited government and open trade.
Republicans who control the White House and Congress also are arguing over how to dismantle and replace President Barack Obama's landmark healthcare law.
Bannon and Priebus both sought to dispel a sense of disorder in the White House portrayed in media accounts.
Referring to media criticism of Trump and echoing the president's attacks on the media, Bannon warned, "It's going to get worse every day" as Trump presses forward with his 2016 campaign promises.
"If you think they're going to give you your country back without a fight you are sadly mistaken," said Bannon, who formerly ran the confrontational right-wing website Breitbart News. He blamed the "corporatist, globalist media that are adamantly opposed to an economic nationalist agenda" under Trump.
The CPAC conference, once a fringe event but is now decidedly in the Republican mainstream, is being held in suburban Maryland, attended by an estimated 10,000 activists.
White House adviser Kellyanne Conway credited Trump with revitalising the Republican Party's right wing.
"Every great movement ends up being a little bit sclerotic and dusty after a time, and I think they (conservatives) need an infusion of energy," Conway said.
Referring to Trump's expected attendance at the conference on Friday, she said, "I think by tomorrow this will be TPAC, this year. No doubt."
