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Among the avalanche of tweets that have so far defined Mr Trump's presidency, one foreign policy issue stands out - North Korea. When ranking the number of mentions by country, North Korea (31) comes second only to Russia (90, although most Russia tweets relate to the US domestic political debate) and it beats China (27) into a close third place. With the president now warning of "fire and fury", we thought it was time for a Reality Check on this constant and evolving insight into his thinking. What does his Twitter feed @realDonaldTrump tell us about the assumptions and beliefs behind his approach to one of the most pressing security issues of our time? So we're training our reality radar on four of his key North Korea messages since being elected. On 5 August 2017, President Trump declared the UN had agreed a sanctions package that would cost North Korea $1bn. This latest set of sanctions, agreed unanimously by the UN Security Council, was heralded by Mr Trump as a diplomatic victory - the culmination of months of work to try to get China on side. There is no doubt that the measures are considerably tougher. They include, for example, the removal of the civilian "livelihood" exemption in the previous sanctions package that allowed North Korea and China to continue trading coal and iron ore in large volumes. But $1bn of difference? Although the figure was supported by at least two other Security Council members (France and Japan), as always the extent of the economic pain inflicted will depend entirely on the willingness of China, North Korea's biggest trading partner, to enforce the new sanctions. Reality Check Verdict: Close enough. The $1bn figure is a best-case scenario, for President Trump, but the sanctions do represent a significant shift, on paper at least. Since his inauguration, President Trump's tweets on China's performance regarding North Korea have veered from high optimism to angry pessimism, and back again. In July 2017, his frustration was front and centre as he tweeted: "Trade between China and North Korea grew almost 40% in the first quarter. So much for China working with us - but we had to give it a try!" This goes right to the nub of the issue of China's enforcement of sanctions. There are some signs that China is beginning to bow to pressure when it comes to general trade, such as commodities. Earlier this year, it did finally stop buying North Korean coal, a major source of foreign currency for Pyongyang, and for the first half of this year, China said its total imports of all goods fell by 13.2%, as reported in the Chinese state newspaper the Global Times. But North Korea is still a long way from being squeezed until its pips squeak. Mr Trump was (almost) right about the 40% increase in total two-way trade with China in the first quarter. The actual figure, according to the Global Times, was 37.4%, although it added that this figure bucked an overall downward trend since 2014, and by May the increase for 2017 so far had dropped to 13.7%. But the same state media editorial makes it clear that pushing Pyongyang to the limit is "not what the UN resolutions are intended to do, nor what the Chinese public wants". President Trump's statements that China could do more are backed up by the views of many other observers. A 2017 UN report linked North Korean rocket components to Chinese companies. There are other credible claims, including one by C4ADS, about the continuing transfer of technology via China. Reality Check Verdict: Spot on. China's stated priority is stability in North Korea, not regime collapse. It is never going to push its old ally too hard. Mr Trump's suspicious barbs are justified. President Trump's tweet in April that if China "want to solve the North Korean problem, they will" is another aspect of his thinking/tweeting that needs testing - his basic premise that, if properly applied, economic pressure might persuade North Korea to give up its weapons programme. Going by North Korea's own words, this seems unlikely. Pyongyang makes it clear via its state news agency KCNA that it sees nuclear weapons as an issue of regime survival. It has learned lessons from the toppling of Saddam Hussein in the non-nuclear armed Iraq, and of Col Muammar Gaddafi after he had given up his weapons programmes in Libya. And it has shown it is nothing if not resilient, enduring a devastating famine during the 1990s throughout which it continued developing its missiles and rockets. The more that sanctions can be made to push North Korea to the brink, and the more alarming and believable the hints of regime change from Washington, the more compelling becomes the logic of a credible nuclear deterrent by which to gain strategic leverage. Reality Check Verdict: Wide of the mark. While sanctions may delay and frustrate North Korea's attempts to gain nuclear-tipped missiles, they are unlikely on their own to stop them. Mr Trump's first tweet about North Korea after his election in November last year set it out as his key foreign policy priority. After North Korea said, in January, that it had successfully miniaturised nuclear warheads that could reach the US, he said "it won't happen". It goes hand in hand with his claim that, in the mission to disarm North Korea, his administration will succeed where his predecessors have failed. What is certainly the case is that North Korea's decades-old nuclear weapons programme has been significantly ramped up under Kim Jong-un and is now at a critical phase. It has startled experts with the speed of its progress, with many now saying it has recently proved it has long-range missiles capable of reaching major US cities. According to information leaked to the Washington Post, US intelligence officials now believe North Korea's claim that it has the technology to fit its missiles with nuclear warheads. Japan's defence ministry has also recently stated this is a possibility. And the varied geographical spread of its test firings has also led to concerns. The Nuclear Threat Initiative has analysed the locations of the tests, and says they could indicate that North Korea is now working in earnest towards rolling out its weapons to missile units around the country in preparation to deploy them. The stakes couldn't be higher, and yet the messages coming from the Trump administration are confusingly mixed. Just a week before Mr Trump spoke of "fire and fury" his Secretary of State, Rex Tillerson, told a press conference: "We're trying to convey to the North Koreans, 'We are not your enemy, we are not your threat.'" Mr Tillerson has also been suggesting that the door to dialogue with North Korea might have been left open a crack. That latter road, of course, would lead to the same set of imperfect choices that has bedevilled every US president since the first George Bush. In the end, all administrations have had to deal with the realities as they find them - a reluctant China, a determined and resilient North Korea and the incalculable cost in human life of any kind of military solution. Many seasoned North Korean observers are hoping that Mr Trump too comes to realise that the reason his predecessors have failed is precisely because there are no easy solutions. Reality Check Verdict: Failed. As for not allowing a nuclear North Korea on his watch, our radar detects that for this particular Trump tweet, it is already too late. Read more from Reality Check Follow us on Twitter

With the rhetoric reaching fever pitch over North Korea's nuclear missile programme, BBC Beijing correspondent John Sudworth turns to Twitter - where else? - to put US President Donald Trump's key messages to the test.