What part of this isn't?
This is not a reasonable interpretation of the president's words. The previous tweet said that the military is standing by. There can be no mistake: Trump is saying that he will order the US military to kill Americans.
That's not an ambiguous sentence.
The thing about Trump supporters that baffles me is, they have the common sense to understand when some his claims are false or hurtful, because they make up excuses for them: they're ambiguous, he was just checking if we were paying attention, etc. even when he refuses to back down and absolutely denies the excuses. But they still enjoy having their prejudices, fears and hates validated whenever Trump's tweets align with their view.