The Panama Canal is an easily achievable mission considering that Panama is a country without a professional army, which is again the result of US policy after the 1990 US overthrew Noriega. As for Greenland, I don't see Denmark giving up even a millimeter in its position that it is its territory, and it has the support of almost all the members of the European Union.
In some crazy development of the situation, Europe could find itself at war with the US and Russia at the same time, and as much as it seems impossible, considering the violent attitude that Donald often shows, and that the new minister looks like a kid who would love to play some military game, all options are open.
Panama appears to be approaching a peaceful resolution. We'll have to see on that. The problem with Greenland is that it is currently undefended and in a strategically important position and Denmark is unable and apparently unwilling to provide a reasonable defense. The people of Greenland are likely to have to pick their poison and hopefully that can be brought to a peaceful resolution.
Speaking of military bases, the problem Europe has is that it has US military bases run through it and a large part of their defense is provided by the US as illustrated when Trump made them squeal when insisting they start meeting their UN commitments. I'm not saying that it's a good thing that the EU being beholden to the US is a good thing but that's the way it it. It makes EU saber rattling somewhat empty. (Just remember how they caved to Bush's lies about WMD in Iraq).