Joe Biden and Holy Communion

It's not really "new". It's just...not the Late Middle Ages anymore.
I disagree. Pope Francis is a mover and shaker and the RCC’s moral position on many topics seems to change more often than Popes before him.
Unlike the Muslim countries, the US has an Establishment Clause, which demands a separation between Church and State.
Therefore, as the US is founded on secular principles, a US president cannot be held to any specific religious tenets and there can be no religious test.

No religious Test Clause
The No Religious Test Clause of the United States Constitution is a clause within Article VI, Clause 3: "The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States." It immediately follows a clause requiring all federal and state office holders to take an oath or affirmation to support the Constitution. This clause contains the only explicit reference to religion in the original seven articles of the U.S. Constitution