The US President Donald Trump has asked his attorney general to investigate who wrote an article that raised questions over his fitness for office.

The anonymous op-ed written by a senior White House staffer detailing how many senior officials are “working diligently from within to frustrate parts of his agenda and his worst inclinations.”

The piece was published in The New York Times.

Earlier President Trump suggested the paper had "virtually" committed treason by printing the article.

This evening, President Trump told reporters: "I would say Jeff [Sessions] should be investigating who the author of that piece was because I really believe it is national security."

He said: "We're going to take a look at what he [the writer] had, what he gave, what he's talking about.

“Also where he is right now."

The US president said if that person had high-level security clearance, "I don't want him in those meetings."

He said he was also looking at whether action would be taken against the newspaper for publishing the article.

"Unsung heroes"

This scathing article "unsung heroes" were moderating the president's "erratic behaviour" and that "the root of the problem is the president's amorality."

"Anyone who works with him knows he is not moored to any discernible first principles that guide his decision making," it said.

The president dismissed the article as "gutless" and a "horrible thing," describing his administration as a "well-oiled machine."

Official denial

Vice-president Mike Pence is one of many senior officials who have denied writing the piece.

Some pointed the finger at Mr Pence because the article used the term "lodestar" - a term he has used before in speeches.

US Secretary of State Mike Pompeo also denied writing it.

Democracy

As the fallout from the article continues, President Obama urged voters to help restore "honesty and decency and lawfulness" to government, saying they were living in "dangerous times."

In a speech at the University of Illinois he called for Democrat voters to make their mark in November's US mid- term elections.

"In two months we have the chance to restore some semblance of sanity to our politics," Mr Obama said.

"There is only one check on abuses of power - and that is you and your vote."

Partisan politics

Mr Obama has previously held back from openly criticising President Trump.

He told students on Friday that his successor was "a symptom, not a cause" of what is dividing the country.

However, he added: "If you thought elections don't matter, I hope these past two years have corrected that impression."

"It should not be a partisan issue to say that we do not pressure the attorney general or the FBI to use the criminal justice system as a cudgel to punish our political opponents," said Mr Obama.

"Or to explicitly call on the attorney general to protect members of our own party from prosecution because an election happens to be coming up.

"I'm not making that up. That's not hypothetical," said the former president.

Meanwhile, the Tánaiste Simon Coveney has admitted the Government was taken a “little bit by surprise” by the announcement that President Trump will visit Ireland in November.

He admitted the visit will be “controversial,” but insisted it would be have been “crazy” for the Government not to facilitate it.