US Free Speech laws are exceptionally broad and, according to Wikipedia, are some of the most liberal in the entire world (I've seen Canadians who, upon realizing American's expectations of what Free Speech means, realize that even Canada Free Speech laws aren't that protective). The TL;DR answer is all four examples are perfectly legal, though not all are socially acceptable.
As a general rule, American Speech laws break speech into three catagories that are listed from least narrow to broadest definition:
Unprotected Speech: Generally this is speech that is not protected by the First Amendment and can be used to show liability in a crime. Note that no specific word or phrase is out and out banned while there is quite a list of speech restrictions, all have some very narrow restrictions placed on them such that the circumstances must be met to consider speech unprotected. Even the classic and oft cited "Shouting 'Fire!' in a Crowded Theater" isn't outright illegal. If there really is a fire in a crowded theater, shouting out the nature of the threat is perfectly legal. While not exhaustive, this list generally holds any speech that incites imminent lawless actions (asking someone to break the law, inciting the mob to violence, fighting words), invoking a "True Threat" (falsely announcing a danger or threat that calls for public action. Dialing 911 to report a non-existent emergency, calling in a bomb threat, threats to inflict harm, etc. all count towards this.) and defamatory statements (Statements which are false and cause damage to the target's reputation.). Obscenities are also found here, but Obscenities are held to be the province of the most local levels of governance in the United States (with exception to Child Porn, at least, but that was specifically carved out by SCOTUS as something that was clearly obscene and the government had a compelling interest to blocking.).
Commercial Speech - Speech that intends to sell a product to a customer. Generally restricted in that the speech must not run against truth in advertisement laws AND certain restrictions on advertising to minors (such as advertising tobacco or alcohol during a commercial break for Spongebob Squarepants or in entertainment geared to Kids.).
Protected Political Speech - The default assumption of all speech made in the United States (You must prove that speech falls in the above two categories during any legal case made against that speech) and protected by the Constitution. It's the broadest and the most expansive of the classes and is so broad, that not speaking is considered protected speech as well. Can also cover non-verbal artistic speech such as paintings or dancing.
Again, in your cases, the first and third examples are clearly discussing politics and the opinion of a voter or other elected official on an elected officer of government and thus is protected. Example 4 is legal but it's acceptability has always been held to for one reason or another but is not illegal (for Cis-gendered, using wrong pronouns can be demeaning as it shows that the individual targeted is behaving like an undesirable member of their sex. Consider the most offensive insult in "The Sandlot" was one boy telling another boy that he "throws [baseballs] like a girl" although the humor of the scene is that the children believe this crosses the line, while an adult would have taken offense to other insults hurdled prior to that one. For Trans individuals, it can be denial of their identity and a sign of disrespect).
Example 2 needs more context... is the buisness owner a crotchety old man who still refuses to say anything truly offensive, but still wants the customer to know he cares for them as much as if they were ducks? Or does the owner work for a company that runs Duck Tours and is calling the customers that because of the company theme?
At either rate, the U.S. is unique among Liberal Democracies in that the U.S. has no "Hate Speech" laws. That is to say that there are no laws criminalizing speech that is offensive to people by protected characteristics. That said, Hate Crimes do exists, which is a charge that can be applied to any crime where it is clear that the victim being targeted for protect characteristics whether they are perceived or otherwise (it doesn't matter if an Anti-Islam mob attacked a Sikh thinking they were Muslim, it still counts. Wrong for the wrong reasons is still wrong.). In this context, slurs may be considered as evidence in and of themselves, but the crime isn't their use in the attack, it's the attack itself.
