18 U.S. Code § 2381 - Treason: "Whoever, owing allegiance to the United States, levies war against them or adheres to their enemies, giving them aid and comfort within the United States or elsewhere, is guilty of treason and shall suffer death, or shall be imprisoned not less than five years and fined under this title but not less than $10,000; and shall be incapable of holding any office under the United States."
That law is based on the U.S. Constitution, where Treason is the only crime defined (3.3) because of a bloody history in England and elsewhere of accusations of treason being used for the (judicial) murder of political opponents and to punish excessively what were really lesser crimes, if crimes at all.
President Donald Trump's joke (?) about treasonous, non-lovers of America (or Donald Trump) included a threat of death or, minimally, loss of office, a hefty fine, and hard time in a Federal prison. As with any figure of speech, it should be understood first literally — an effective metaphor should get hearers picturing it — and then walked back into the figurative to establish a range of meanings.
E.g., "I demand 110% dedication to the team" is obviously hyperbole: there can't be more than 100% of anything, and people who'd give 100% dedication to any one thing would need an impossible amount of spare dedication on their hands. But how much dedication does Coach demand? Unclear. S/He wants a figurative blank check.
If Trump doesn't literally want those who don't applaud him at the State of the Union Address tried for treason and executed, what punishment does he want for them? Another (figurative) blank check, of the bullying-threat variety.