The widely-circulated "nuclear" theory suggests China would dump US treasuries in a trade war with the US. That theory never made any sense. Such a move would tend to strengthen the yuan, making Chinese exports more expensive. Thus, it would be precisely what the US would want.
The Real Nuclear Option
The real nuclear option would be a devaluation of the yuan, making Chinese goods less expensive to the US.
Reportedly, China is Studying Devaluation.
China is evaluating the potential impact of a gradual yuan depreciation, people familiar with the matter said, as the country's leaders weigh their options in a trade spat with U.S. President Donald Trump that has roiled financial markets worldwide.
Senior Chinese officials are studying a two-pronged analysis of the yuan that was prepared by the government, the people said. One part looks at the effect of using the currency as a tool in trade negotiations with the U.S., while a second part examines what would happen if China devalues the yuan to offset the impact of any trade deal that curbs exports.