There are three plausible reasons why China has responded this way so far. First, Chinese leaders may believe that negotiation at this stage will not produce a satisfactory outcome. They regard the US approach as akin to a kidnapper: any concession could just invite more hostage-taking. After all, China already abstained from responding in kind to two earlier rounds of incremental (10%) US tariffs, on February 1 and March 3, and that did not prevent Trump from adding another 34% levy on April 2.
China has taken a tough stance against US President Donald Trump, matching the last two rounds of US tariffs with tariffs of its own. The US tariff on goods from China is now 145%, while China’s is 125%. Why does China take such a position, and are there any off-ramps that would allow it to mitigate the costs of a prolonged trade war?

