A former US labour secretary has warned Donald Trump’s attacks on the media could be leading America down a “slippery path” to censorship.

Robert Reich, who served under Bill Clinton from 1993 to 1997, said the US President’s “increasingly incendiary tweets” aimed at the media “constitute an overt assault on the freedom of the press.”

The long time critic of the US leader warned that while claims Mr Trump could be mentally unwell may still prove to be true, he feared “an even more menacing reality”.

“His new attacks seem to be going a step farther, mobilising his supporters against media personalities and executives that are critical of him,” Mr Reich wrote in an op-ed for Alternet.

His comments come days after Mr Trump shared a piece of edited wrestling footage that showed him flooring a figure whose head had been replaced by a CNN logo.

Mr Reich wrote: “Will news organisations be intimidated? Probably not, at least not at this point. But we may be on a slippery path. Trump’s increasingly incendiary tweets and messages constitute an overt assault on freedom of the press, the cornerstone of our democracy.”

Mr Trump was heavily criticised after sharing the CNN wrestling clip, with media pundits accusing him of inciting violence.

In pictures: President Donald Trump on tour Show all 39 1 /39 In pictures: President Donald Trump on tour In pictures: President Donald Trump on tour 20 May 2017 US President Donald Trump and Saudi Arabia's King Salman bin Abdulaziz al-Saud arriving for a reception ahead of a banquet at Murabba Palace in Riyadh Getty Images In pictures: President Donald Trump on tour 20 May 2017 US President Donald Trump, accompanied by First Lady Melania Trump, and Saudi Arabia's King Salman bin Abdulaziz al-Saud being welcomed at Murabba Palace in Riyadh Getty Images In pictures: President Donald Trump on tour 20 May 2017 US President Donald J. Trump with King of Saudi Arabia Salman bin Abdulaziz Al Saud during a welcome ceremony with traditional sword dancers at Murabba Palace, in Riyadh, Saudi Arabia EPA In pictures: President Donald Trump on tour 20 May 2017 King of Saudi Arabia Salman bin Abdulaziz Al Saud with US President Donald J. 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Mr Reich said the president's narrative was increasingly aligning with the kind of content shared on right-wing websites.

“As the tweets and rallies become shriller and more provocative, their clear message is that Trump’s critics are bad people who are conspiring to undo his presidency – people whom Trump supporters must “not let” silence him, who deserve to be slammed the way Trump took it out on CNN in the mock video he posted Sunday morning,” he wrote.

“It’s a narrative that’s showing up increasingly on right-wing websites.”

It comes after a new poll found Americans continue to trust the media more than Mr Trump.

Asked whether they trusted the President or CNN more, SurveyMonkey respondents chose the news network over the US leader by a margin of 7 per cent.