> No, congress would have to declare war first. Article I, Section 8.
Article I, Section 8 gives Congress the sole power to declare war, it does not, on its own, prohibit any other action than "declaring war" to any other actor.
The War Powers Act (or Resolution) attempts to put some additional rules around this (note that it is widely seen as being either an unconstitutional intrusion on Presidential authority or an unconstitutional delegation of Congressional authority, and courts have so far failed to resolve it, having found lack of standing in the few cases that have been brought under it.)
But even the War Powers Act doesn't purport to prohibit the President from using force in advance of Congressional authorization.
Only in the second gulf war did the US become an occupying force, and this action was permitted by congress. The others may have been “invasions” but certainly not occupations or annexations. I could be wrong, but I don’t see congress allowing Trump to destroy NATO.
It would still require congressional approval after 60 days, unless Al Qaida suddenly showed up in Greenland. Despite congress being majority R, I just don’t see them playing along with this.
Trump says these things to get a rise out of people. He’s fueled by reaction. You can’t tell if he’s ever being serious, and I doubt even he knows if he’s being serious most of the time. Getting enraged by his actions is his goal, and he’s very good at playing his opponents into blunders this way. Best to not play along.
> It would still require congressional approval after 60 days
"After 60 days" is very different from "first".
And, since the President can unilaterally extend the timeline by 30 days, its actually 90 days, even if the War Powers Act is valid (an unresolved Constitutional question.)
And, in practice, it doesn't even require that if you don't have active majorities in Congress opposing the action; see the NATO-Yugoslavia war and the failure of legal challenges by members of Congress against it predicated on the War Powers Act limitations, because of lack of standing.
If invading Greenland was an actual real goal, something like this would definitely "happen", to manufacture the necessary pretext. Way cheaper than the alternatives.
