A Strawman argument! The distinction about citizens is made before any mention of immigration status (as you, yourself note in what you quote). "If you are a citizen of the United States," preempts any further considerations in the letter. Your argument is a non sequitur.
The legal fact of the matter is that simply being a U.S. citizen does not automatically give you the right to vote in a Federal election and being an immigrant and being a citizen are two separate issues under the law.
A convicted felon that is a U.S. citizen does not have the right to vote.
A 17 year old U.S. Marine that is a U.S. citizen does not have the right to vote.
If you advise that 17 year old U.S. Marine that, "If you are a citizen of the United States, we ask that you participate in the democratic process of voting" you are advising the 17 year old U.S. Marine to commit a crime.
An immigrant can become a U.S. citizen but the fact that he is an immigrant rather than native born is a point of law that even the Constitution addresses in Article II, Section 1 as a disqualification for ever being President of the United States.
Under U.S. law, the rights of native-born U.S. citizens and immigrant U.S. citizens differ precisely because you can be both an immigrant and a citizen.
"U.S. citizen" and "individual entitled to vote" are not legally synonomous phrases.
In addition, "citizen" and "immigrant" are not legal antonyms.
This man was threatening U.S. citizens who were immigrants about "jail time" and "deportation" if they voted in a Federal election in violation of the intimidation provisions of the Voting Rights Act.
If you ever try to intimidate a U.S. citizen from exercising a civil right guranteed under law by threatening "jail time" or "deportation" or whatever other threat you want to throw in, you had better ensure that your legal wording and your legal logic is impeccable and that you can carry out that threat in a court of law EXACTLY as you phrased it.
If your threats can be excused only by having your attorney explain to the Judge, "what my client actually meant to say", you have a good chance of ending up with jail time yourself.
Criticizing the use of language (in either language) is hardly the principal issue ... that is being a lawyer. Sufficiently precise text that would satisfy any lawyer would likely be turgid to the point of being unreadable to any average reader (whatever their language).
Might it be assumed that the specifics of voter eligibility among citizens is not the issue of the letter?
The issue of the letter is to remind non-citizens (some of which have recently been told they CAN vote or that they have a "moral right" to break our laws) that they do not have the right to vote no matter their legal status.
As for threatening citizens ... any naturalized citizen may be assumed to have a bit better grasp of the laws governing voting than the average native IF ONLY because they have had to demonstrate that knowledge before gaining citizenship––at least to some degree. I would contend that a naturalized citizen who is not plagued by the American Disease––Offensensitivity––would likely recognize the distinction that I pointed out ... the letter first addresses "citizens" and encourages them to vote.
To do so doesn't imply that all citizens CAN vote ... only that it is citizens that can vote in federal elections.
As for the law, you are right to point out that voting is a privilege and not an automatic right. While I'm not aware of every point of law (who could be?) and I am concerned that numerous "civil rights" have been enumerated under the abuse of the Commerce Clause: I fully recognize that the "privileges or immunities" clause of the 14th Amendment was designed to empower Congress to enumerate defined civil rights which the several States cannot disparage (and by extension those civil authorities under the States).
But the burden on a state, elected or civic official ACTING as such, and the burden on a Person are not one and the same. No aspect of the Constitution empowers Congress to enumerate civil rights which Persons cannot disparage––which was the subject of the landmark Civil Rights Act Cases decision.
Now, that decision was the right one; however, the opinion is lamentable and abominable.
Simply, Justice Bradley's opinion lacked the nuance to recognize that Persons ACTING as officials of a State (be they administrators, legislators, judges, or law enforcement) are in fact agents of the same and cannot disparage civil rights enumerated by Congress in their official capacity.
Had Justice Bradley's opinion had even that much nuance––rather than being an ideological bag-o-hammers––then the very worst of Segregation and Jim Crow––in matters of public accommodations like schools––would have ALWAYS been illegal since there IS a limited and yet important domain in which the Civil Rights Act of 1875 is––or should have always been––constitutional.
However, to say that federal law can restrict what an official may do––as in this case––and what a private Person can do is entirely two different things. It is just as unlawful for certain individuals to have encouraged illegal aliens TO VOTE as it would be for an official to discourage ("intimidate" to use your term) legal voters from exercising their right.
However, the same IS NOT true of private Persons PROVIDED they do nothing beyond spreading misinformation or the like. This is because a private Person encouraging someone who can't legally vote to vote is encouraging the commission of a crime while his counterpart is simply being a reprehensible JERK.
The Constitution essentially protects the right of private citizens to be jerks ... which is probably good news for many of us folks obsessed with politics. ^_^
This man was threatening U.S. citizens who were immigrants
What evidence do you have that he had anything to do with this? You're already declaring him guilty. Have you not heard of "Innocent until proven guilty?" It appears not.