Why is Trump talking about nuclear weapons?

Less than an hour before Donald Trump met the Chinese president, Xi Jinping, to discuss a deal that could end the trade war between the two superpowers, the US president posted on Truth Social that he had directed the Pentagon to match Russia and China in nuclear weapons testing. Jonathan Freedland speaks to <a href="https://www.brookings.edu/people/jonathan-a-czin/" rel="nofollow">Jonathan Czin</a>, the former director for China at the National Security Council, about why Trump did this and whether he or Xi left South Korea feeling the strongest