Sky Views: North Korea will keep Trump up at night

Katie Stallard, Asia Correspondent

As Donald Trump remains focused on his travel ban and the "peril" from which he insists it will save the American people, North Korea appears to have quietly restarted its nuclear reactor.

Recent satellite imagery analysed by the 38 North monitoring project shows operations have likely resumed at a plutonium facility at the country's main nuclear site.

Last month, Kim Jong-Un said the country was in the final stages of preparing to test launch its first intercontinental ballistic missile - a further step towards his declared goal of a nuclear weapons system capable of hitting the US mainland.

"It won't happen," Mr Trump tweeted in response, but he has yet to lay out any of his thinking as to how he intends to go about thwarting this - beyond tweeting angrily at China that they "won't help with North Korea. Nice!"

The real question is how to stop Pyongyang's weapons programme before it gets to that point - before the decision on whether to launch a long-range nuclear missile comes down to the judgement of Kim Jong-Un.

His new Defence Secretary, James Mattis, flew into the region last week on what was widely seen as a mission to reassure American allies.

Reassurance was needed after Donald Trump's comments on the campaign trail. He openly questioned the value of the alliances - telling Japan and South Korea they would have to pay more for the US security guarantee. At one point, he appeared to suggest they should think about getting their own nuclear weapons.

Mr Mattis duly carried out his mission, assuring Japan and South Korea that the US commitment was "ironclad" and that any use of nuclear weapons by North Korea would be met with an "overwhelming response".

It made for good headlines, and sounded suitably tough, but was really just a restatement of the status quo.

Let's assume Mr Kim already understands that actually using any of his nukes would be met with devastating, likely regime-ending force. Maybe it's one of the reasons he is developing submarine and mobile launching capabilities, to improve the chances of surviving what would surely be a monumental second strike.

The real question is how to stop Pyongyang's weapons programme before it gets to that point - before the decision on whether to launch a long-range nuclear missile comes down to the judgement of Kim Jong-Un.

During their presidential handover, Barack Obama reportedly warned Donald Trump that the most serious threat to national security he will face may be North Korea.

His own policy of "strategic patience" has not worked, and the options now before the Trump administration are as unpalatable as ever.

Sanctions haven't stopped the Kim regime so far, and may just cause it to cling ever tighter to its warheads. Concessions risk the appearance of caving in to nuclear blackmail, and military force would put 10 million civilians in Seoul in artillery range of a retaliatory strike.

Add to this the current political turmoil in South Korea, where the president has been impeached, and early tensions between the new US administration and Beijing over Taiwan and the South China Sea.

Then there is the planned US-South Korea missile shield deployment, which China hates, and North Korea says is pushing the peninsula "to the brink of a nuclear war".

Mr Trump likes to boast that he doesn't need much sleep. He certainly seems to be up and tweeting into the early hours.

As and when he turns his attention to the Korean peninsula, there is plenty more to keep him up at night.

Sky Views is a new series of comment pieces by Sky News editors and correspondents, published every morning.

Previously on Sky Views: Paul Kelso - Chelsea charge embarrasses Mourinho