The news that only around half as many mainlanders are coming to the US to study now as before the pandemic seems a harbinger of worse to come.

【1】句子主干为：The news seems a harbinger of worse to come

【1】that only around half as many mainlanders are coming to the US to study now as before the pandemic 为连词that引导的同位语语从句，作主语the news的同位语。

以上句子整体语法结构分析如下：供网友参考

The news【主语】//  that only around half as many mainlanders are coming to the US to study now as before the pandemic 【同位语】// seems【系动词】//  a harbinger of worse【表语】//  to come【后置定语】// .

备注(2):to come不定式作后置定语修饰前面的名词短语a harbinger of worse。