Bradley Bowman (who advised republican senators on foreign policy) says what （he expects） a Biden presidency would mean, you would see continued emphasis on encouraging our European...

划线部分为says的宾语从句。该宾语从句为嵌入式名词性关系分句。即宾语从句本身又是一个带有宾语从句的主从复合句，其中he expects为主句，what a Biden presidency would mean这个名词性关系分句为宾语从句。what是名词性关系分句的宾语。

you would see continued emphasis on encouraging our European...这个分句为补充语，对what作补充说明，其前的逗号等于破折号或冒号。