"Jim Acosta has our full support".
The president turned away, trying to go on to another reporter, but Acosta refused to give up his microphone.
Peter Baker from The New York Times, who has been covering the White House for 22 years, said, "This is something I have never seen since I started covering the White House in 1996".
In two separate tweets, he said: "I've just been denied entrance to the WH".
Acosta then badgered the president, asking, "Did you demonize immigrants?" Acosta said before Trump interrupted him.
In response, Acosta said, "This is a lie". He said Acosta held on to the microphone as the intern reached for it and later posted a few pictures from the press conference to prove his point.
"Well, I'm not a big fan of yours, either", the president of the United States actually said.
During the event, the president refused to answer Acosta's questions about indictments in the Russian Federation investigation, saying, "I'm not concerned about anything with the Russian Federation investigation, because it's a hoax".
"I think you should let me run the country, you run CNN", said Trump. It's a very awful thing that you said".
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Chris Watts kept changing stories after his pregnant wife and two daughters disappeared from their Colorado town in mid-August. Chris Watts , 33, has pleaded guilty to murdering his pregnant wife and their children in a case that shocked the world.
Looking back at Acosta, Trump added: "The way you treat [press secretary] Sarah Huckabee is terrible, and the way you treat other people is awful. You shouldn't treat people like that".
Alexander came to his colleague's defense. He added in another tweet that he didn't "blame" the U.S. Secret Service agent who stopped him.
"I understand", Mr Alexander said, attempting to ask a question. "It's so sad", Trump said. "When you report fake news, as CNN does a lot, you are an enemy of the people".
After the exchange, CNN, through its public relations department's Twitter feed, said Trump's attacks on the press have gone too far.
US President Donald Trump got into a tense and charged verbal argument with a journalist last night that led to the reporter's press credentials being suspended. He was heading back to the White House for a live shot on "Anderson Cooper 360".
Mr Trump made several references in his news conference to how he feels mistreated by the press. "Honestly, I know you have it written down, that's a racist question". He doesn't like that there are some white nationalists who are supporting the president. Those were reporters working with CNN, NBC, other networks. "What would I do without you?" You are a very rude person.
Alcindor moved on to a different topic.
The president began the wide-ranging press conference with a focus on the election results, but it soon devolved into brazen and shocking media attacks that appeared created to frustrate and enrage the president.
Mr Trump took the rare step of mocking Republican candidates who kept their distance from him during the campaign because of concerns that his divisive messages on immigration would turn off voters - but lost anyway.