Video footage and photographs showed the intern grazing Acosta's arm in trying to pry the microphone away, and briefly making contact with the hand holding the microphone.
Later she tweeted a 15-second video of the exchange, including close-up replays, in which the sound appears to have been silenced.
The White House Correspondents' Association is denouncing the decision to bar Acosta, calling it unacceptable and disproportionate to the purported offence.
"We will not tolerate the inappropriate behaviour clearly documented in this video", Sanders said, posting a video of the CNN reporter allegedly placing his hand on a young woman.
"We have been working at the White House for five years covering two administrations", Acosta said to the officer, as he voluntarily gave up his hard pass.
On Twitter, Acosta responded to Sanders' statement with a simple declaration, tweeting: "This is a lie".
Wednesday's event, which began with the president framing Tuesday's election results as a victory for himself and the Republican party, was Trump's first planned, open-ended press conference at the White House since February 2017, and only the second since he took office.
"This president's ongoing attacks on the press have gone too far".
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This news comes after Rihanna posted her endorsement of Florida Democratic gubernatorial candidate Andrew Gillum on Instagram . One singer, however, was less than thrilled to learn that the president had also been using her music without permission.
They began sparring Wednesday after Acosta asked Trump about the caravan of migrants heading from Latin America to the southern United States border.
During the exchange, the staff member is seen approaching Acosta before attempting to take the microphone off him.
Looking back at Acosta, who again rose up in his own defense, Trump added: "When you report fake news, which CNN does a lot, you are the enemy of the people".
"CNN should be ashamed of themselves, having you work for them", he said. The way you treat Sarah Huckabee is disgusting, and the way you treat other people are frightful. You're a very rude person.
"Secret Service just informed me I can not enter the grounds for my 8 pm hit", Acosta tweeted Wednesday evening.
Mashable has reached out to the White House for comment on the allegations surrounding the video Sanders shared. It is also completely disrespectful to the reporter's colleagues not to allow them an opportunity to ask a question", she said on "Trish Regan Primetime. "You are a rude, awful person".
At that point, a White House intern tried to physically take the microphone from Acosta, who wrestled them for it. 'Excuse me ma'am, ' he said to her.
He said that until the revocation, Sessions' departure was likely to be the topic of Acosta's and others' reporting this evening.
"They are not only risky, they are disturbingly un-American", CNN said. You and I disagree on this, ' Trump said.
Sanders said Trump has given the press more access than any President in history. "You run CNN", Trump fired back.