1911-1913 very shady time in USA political history. They could amend the Constitution to make a law Constitutional.
There's nothing shady about that in the least. In fact, it is the point of constitutional amendments: to provide a mechanism to change the constitution when it prohibits something that an overwhelming majority of people -- well, of congress ...
To understand the Constitution, use Samuel Johnson's dictionary.
Johnson defines "to Ataint" as:
To attaint is particularly used for such as are found guilty of some crime or offence, and especially of felony or treason. A man is attainted two ways, by appearance, or by process. ...
They appear to specifically address this in this section:
SEC. 223. REPEAL OF LAW PROVIDING FOR PARTICIPATION OF SEAT OF GOVERNMENT IN ELECTION OF PRESIDENT AND VICE-PRESIDENT.
What this does is remove the District of Columbia from the definition of a "state" as it applies in the USC chapter dealing with Presidential elections. Since the 23rd ...
"No taxation without representation!" was a slogan of the US war of independence, but it was never put into the Constitution. Indeed, the residents of the District of Columbia and Puerto Rico now pay Federal income tax, but are not represented in the Congress that sets the taxes.
National debt has some of the same economic effects of a tax, but ...
You don’t have to swear
Witnesses are given the option to swear (technically take an oath) or to affirm, which has no religious connotations. You also don’t actually swear on a Bible if you do swear. For example california.
The US is a very religious state
france is a secular state - it prohibits religious clothing (hijabs, crucifixes etc.) in schools.