Donald Trump

He will replace Lt Gen Michael Flynn who was fired after just three weeks and three days in the job.

A lieutenant general with the US Army, HR McMaster served in Iraq and Afghanistan, where he worked on a government anti-corruption drive.

Mr Trump's first choice, retired Vice Admiral Robert Harward, turned down the role, citing "personal reasons".

Who is Lt Gen HR McMaster?

Craig Deare was removed from his role as a senior adviser at the National Security Council's Western Hemisphere division Friday and "sent back to his original position," said Sarah Sanders, a White House spokeswoman. Deare had been assigned to the NSC by the Trump administration.

In his first month in office, Trump has found the vast government machine can't be reset at a president's whim with the same ease that an executive can manage a business. Rival power centers in the courts, the bureaucracy and Congress can emerge as a threat at any point.

The hacked server, secure2.donaldjtrump.com, which isn’t directly linked to the campaign’s home page, is behind CloudFlare’s content management and security system, Ars Technica reports.

The certificate of the server is legitimate and it looks like a real Trump campaign server. However, the image displayed is linked to some other website. The picture shows the following text:

Addressing a rally on Saturday, he had said, "look at what's happening last night in Sweden", as he listed parts of Europe hit by terrorist attacks.

With no such incident reported in Sweden on Friday, the country asked the US administration for an explanation.

Mr Trump tweeted on Sunday that he had been referring to a TV report.

He said it had been broadcast on Fox News but did not say when. He may have been referring to a Fox News programme on Friday night, which looked at refugees and crime in Sweden.

He has selected four candidates: adviser Keith Kellogg; former UN ambassador John Bolton; Lt Gen H R McMaster; and Lt Gen Robert Caslen.

The role became vacant when Lt Gen Michael Flynn was fired after just three weeks and three days in the job.

Mr Trump's first choice, Retired Vice Admiral Robert Harward, turned down the role, citing "personal reasons".

Gen Flynn stepped down after misleading Vice-President Mike Pence over his conversations with Russia's ambassador to the US.

Trump referenced the Scandinavian nation, known for liberally accepting Syrian refugees, during a section of his speech decrying the dangers of open borders.

"We've got to keep our country safe," he said. "You look at what's happening in Germany. You look at what's happening last night in Sweden. Sweden, who would believe this? Sweden. They took in large numbers. They're having problems like they never thought possible. You look at what's happening in Brussels. You look at what's happening all over the world. Take a look at Nice. Take a look at Paris."

"There is a question that in a time of crisis, where will America be?" Kasich told CNN's Jim Sciutto on "State of the Union," referring to what world leaders are saying.

Kasich, a two-term Republican, said Vice President Mike Pence, Defense Secretary John Mattis and others have reiterated the United States' commitment to key alliances and organizations like NATO.

Now, some internet users have gone one step further and doctored images to make his whole body look minuscule.

At 6ft 2in (187cm), Mr Trump is taller than many world leaders and edges ahead of his predecessor, Barack Obama (6ft 1in - 185cm).

But numerous images have been doctored to make him look tiny, as Reddit users attempt to provoke him to respond.

Trump, who just months ago finished campaigning for the office he now holds, was both selling what his administration has done in its first 30 days and trying to change the subject after a chaotic month. The President was forced to fire his national security adviser, struggled to roll out his travel ban and strained to explain a growing story about how members of his 2016 campaign made repeated contact with Russian individuals known to US intelligence.