The bigger question is does the POTUS need Congressional Approval to invade and overthrow the non aggressive nation of Greenland and if done without Congressional Approval is it an impeachable act.
Looks like we're going to find out.
Congress is inept and doesn't know their back side from deep center field
It's actually ironic. Trump could easily get around Congress to take military action to realize our inherent logical claim to Greenland. Trump would actually require Congress to do it the slower more diplomatic way of negotiating a purchase agreement or some sort of new treaty that could render Greenland into a sort of shared territory or special economic zone within NATO/EU. This ironically creates a perverse incentive actually to go the route of military action since it is technically more expedient and has less chance of being subverted by bad faith actors and the myopic ones that really just want to subvetrTrump and/or the State rather than genuinely parse this high political issue. Though I would note Trump still, at least for now, maintains the more diplomatic route though Europe foolishly kinda denies this or responds with passive aggressive threats and insults rather than think a little bigger and put their ridiculous egos aside for a minute to think creatiely and try to accomodate our vision and also benefit mutually themselves.