Vatican City is a country. The Pope is the head of state. Presidents visit heads of state.
The Johnson amendment to the Internal Revenue Code of 1954 makes organizations endorsing a political candidate or intending to influencing legislation to be ineligible for 501(c)(3) tax exempt status.
501(c) is the most common type of tax exempt charitable organization. Many of you probably belong to one in the form of a church, a sportsman's club, Rotary, etc.

(3) Corporations, and any community chest, fund, or foundation, organized and operated exclusively for religious [ . . . ] purposes [ . . . ] no part of the net earnings of which inures to the benefit of any private shareholder or individual, no substantial part of the activities of which is carrying on propaganda, or otherwise attempting, to influence legislation (except as otherwise provided in subsection (h) [relating to certain expenditures by charities to influence legislation]), and which does not participate in, or intervene in (including the publishing or distributing of statements), any political campaign on behalf of (or in opposition to) any candidate for public office.

This applies to your churches and temples and their representatives/leaders in that capacity.
It does not apply to a foreign head of state. The Pope, the Chancellor of Germany, and the Queen of England can say whatever he/she wants and do so in front of God and everybody; it doesn't violate US law.

Atheists or Scientologists or whatever you call yourselves are a bunch of snowflakes that can't handle someone else having a different beleif - kind of like socialists and Nazis. The constitution guarantees freedom from a state sponsored religion, i.e. the Church of England, and freedom to practice, or not, any religion you wish, or do not. It does not guarantee freedom from seeing a symbol of a religion nor the right to ban or interfere with the free practice of another's religion. Snowflakes that can't handle seeing a cross, well, share a safe space with the lady who flips out when she sees a confederate flag.

The New Atheist Movement wants to remove, counter, and destroy religion. Guess what? The intelligentsia leaders of the New Atheism are socialists and communists who want to destroy the Constitution.
Take freedom to practice away, take away free speech, firearms, freedom from search and seizure. It's all the same guys, it's taking away someone's rights. Maybe I should pick and atheists lose freedom of speech and the 2nd amendment because it