Current chip shortage is not caused by not being able to build fab buildings fast enough: it is caused by not being able to buy enough of the lithography machines to put in the buildings. (The machines take years to build.) Where are these litho machines made? Europe, Japan and the US. If mainland China makes any at all, they are decades behind the state of the art.

Point is that China's supply of chips is much more precarious than the US's because all the US has to do at the start of any hostilities with China is to make it clear to the countries that export these litho machines that the US will not tolerate any exports of the machines to China.