最简单的方法是从
the extent to which it has become a political liability for the White House.
的问句开始,
这个句子的问句是
To what extent has it become a political liability for the White House?
句子的倒装形式就是
the extent to which it has become a political liability for the White House.
（倒装句 不用 to what ,而必须用 to which .）
再举两个类似例子：
In what way is the invention useful?
倒装形式：
The way in which the invention is useful is ...
On what grounds are you justifying this action?
倒装形式：
The grounds on which I justify this action are ...
这是弄清楚短语
to which,in which,on which 等等
的用法的唯一方法.