It's still perfectly legal to want the President dead. You just can't say you want it to happen. Speaking isn't a thought, it's an action.
Actually, you can legally say that you want it to happen, at least based on my understanding of the law in question. Where it becomes a crime is when there is both an expressed desire to actually cause that harm (or a call for others to do so) and a reasonable expectation that it might be feasible for you (or those others) to do so in the manner suggested.
Here are a couple of examples that illustrate the difference:
Lack of intent: In theory, you could legally say that you wish the President would get beaten to death by a gang dressed in clown suits while smoking bananas and drinking cheap beer. If you did so, such a statement would not be committing a crime, because wanting someone to die is not the same thing as threatening to kill someone.
With that said, if someone actually expressed such an interest, the Secret Service would take a very close interest in that person's background, looking to see if (for example) he or she had ever bought a clown costume, bananas, or cheap beer.
Additionally, it should be noted that if you then went on to say, "And if I ever get the chance, I'll be part of that gang," then you would almost certainly go to prison, because that statement of personal intent would cross the legal threshold for being a threat. Similarly, if you asked others to harm the President, or said things that appeared to advocate the assassination of the President, that would also be considered a true threat.
- Implausible means: Most people could legally say that they want to hit the President with a giant meteor from space without committing a crime, because to the best of my knowledge, even our best scientists have no real means of making a meteor fall on the White House, much less some random person who has never had any affiliation with any space program whatsoever. With that said, if you are affiliated with NASA, such a statement might be seen as a threat. Maybe.
Additionally, the following conditions must all be met before something is considered a threat:
- The threat must be made intentionally, not accidentally.
- The context and manner of the threat must be such that a reasonable person overhearing it would assume that it was an actual expression of intent to harm the President. (For example, snarky comments at a political rally or in a stand-up comedy routine are not likely to be seen as legitimate threats.)
- The threat must not be made under duress, and must not be forced.
Of course, you can easily get into grey areas, and if you do, even if you don't get jail time for it, you'll probably get a lot more scrutiny than you'd like.
Finally, I'd like to add that IANAL, and this post should not be taken as legal advice.