WASHINGTON (NYTIMES) - In naming Mr Stephen K. Bannon to a senior White House post, President-elect Donald Trump has elevated the hard-right nationalist movement that Mr Bannon has nurtured for years from the fringes of American politics to its very heart, a remarkable shift that has further intensified concern about the new administration's direction.

The provocative news and opinion website that Mr Bannon ran, Breitbart News, has repeatedly published articles linking migrants to the spread of disease. Its authors have criticised politicians who do not support a religious test for immigrants to screen out potential militants. And it has promoted stories that try to tie Ms Huma Abedin, a top aide to Mrs Hillary Clinton who is Muslim, to Islamic militants.

In an interview, Mr Bannon, 62, rejected what he called the "ethno-nationalist" tendencies of some in the movement. His interest in populism and American nationalism, he said, has to do with curbing what he sees as the corrosive effects of globalisation. And he believes his enemies are misstating his views and those of many Trump followers.

"These people are patriots," he said. "They love their country. They just want their country taken care of."

"It's not that some people on the margins, as in any movement, aren't bad guys - racists, anti-Semites. But that's irrelevant," he added.

Mr Bannon's ascent has quickly become the focus of Mr Trump's critics, who broadly condemned the choice as divisive, if not racist, on Monday (Mov 14). But it was also a victory of head-spinning dimensions for Mr Bannon. When he joined Mr Trump's sputtering presidential campaign in August, he insisted to his friends that even if Mr Trump lost, he could at least mitigate any damage to the nationalist movement, which he helped fuel as the head of Breitbart.

Instead, that nationalist movement - it has promoted or enabled anti-immigrant, anti-Muslim and racist sentiments - will now have a champion at Mr Trump's side in the West Wing. Mr Bannon will have the opportunity to shape domestic and foreign policy for a president who is taking office with few positions detailed.

The place that Mr Bannon will occupy in the new administration, as senior counselor and chief strategist to the president, also elevates someone whose mission in politics has been to tear down institutions, not run them, to one of the most powerful roles in the government.

Mr Bannon's appointment was intended to be a reassuring signal to the vocal and restive part of Mr Trump's populist, anti-Washington base that is suspicious of power and anyone who holds it. Mr Trump is their champion, but Mr Bannon is their check against the Washington establishment and any efforts it makes to soften the new president's resolve.

Mr Bannon has told people in Mr Trump's inner circle that the new administration will have a short window of time to push its agenda through and should focus first on the priorities that are expected to be the most contentious.

His influence may be felt initially on the Trump administration's approach to issues like immigration and government ethics reform, which, as chief executive of the Trump campaign, he helped shape as central elements of Mr Trump's message.

Mr Bannon, whose career has included jobs as a Navy officer, a Goldman Sachs banker and the chairman of Breitbart, is expected to be an unrelenting advocate of many of Mr Trump's most aggressive plans on immigration. That involves stopping the immigration of Syrian refugees, deporting unauthorised immigrants with criminal records and devoting more resources to securing the border.

He has reassured those close to him that he will maintain the direct line to Mr Trump that he enjoyed during the campaign and that he will be on equal footing with Mr Reince Priebus, who will have the more visible job of White House chief of staff and an appointee who comes directly out of the Republican Party establishment. The question of how Mr Bannon and Mr Priebus will work together - or if they can - is one of the largest facing the new White House.

Mr Bannon, who grew up in a working-class neighbourhood in Norfolk, Virginia, earned degrees from Georgetown and Harvard. He often compares Mr Trump's political rise to that of Andrew Jackson, the military general and populist hero who took on the political and social elite of his day as the seventh president of the United States.

Mr Bannon's disgust with the politics of the mainstream Republican Party burns just as hot, if not hotter, than his animus toward liberals. He sees Republicans as the "party of Davos donors" and has scorned them for denigrating Trump supporters as the "vulgarians, the hobbits" and "the peasants with the pitchforks."

While Mr Trump became the leader of the movement of disaffected Americans who feel lost and disenfranchised in a nation undergoing rapid cultural and demographic change, Mr Bannon has been a student of global populist trends, carefully tracking the rise of the far-right National Front in France under Marine Le Pen and the remarkable victory of the U.K. Independence Party in Britain's vote this year to leave the European Union.

"Steve saw - and was a thought leader and a visionary about - the issues and the movement that Trump eventually caught onto and espoused," said Mr Larry Solov, the chief executive of Breitbart.

"He's like a field general," he added, "and very much sees the fight for the soul of this country as a war."

But the fight, at times, has become one with overt racial hostility, fed by websites like Breitbart under Mr Bannon's direction and by Mr Trump himself. Breitbart has been especially harsh in its coverage of immigrants and refugees, particularly those from the Middle East and Central America.

Mr Bannon will take his White House job already at odds with House Speaker Paul D. Ryan, an ally of Mr Priebus' who Mr Bannon has long sought to undermine. When he ran Breitbart, Mr Bannon promoted Mr Ryan's opponent in the Wisconsin primary in the website's news stories and radio interviews. Mr Bannon is personally close to members of Congress like Rep. Dave Brat, R-Va., who unseated Eric Cantor, the former majority leader. He has written that the appropriations process under Mr Ryan was "a total and complete sellout of the American people."

His former colleagues at Breitbart refer to him admiringly as a "honey badger" because of his relentlessness, which they say they expect him to use against Republicans and Democrats in equal measure.

"What drives Steve," said Mr Joel B. Pollak, Breitbart's editor at large, "is the way the political establishment is holding back American politics." Mr Pollak added, "He has absolute clarity about what needs to be achieved at any given time."