except as 的用法

题目

except as 的用法
Section 4.The times,places and manner of holding elections for Senators and Representatives,shall be prescribed in each state by the legislature thereof； but the Congress may at any time by law make or alter such regulations,except as to the places of choosing Senators.
各州州议会应规定本州参议员及众议员之选举时间、地点及程序 ； 但国会得随时以法律制定或变更此种规定,惟有选举议员的地点不在此例.
请问“except as to the places of choosing Senators” 里面的“to”可不可省略不用?为啥这么用?

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