Mika Blujan-Mared

European leaders consider Trump's talk of acquiring Denmark's autonomous territory of Greenland and threatening to use sanctions on any country that stands in his way as crossing a red line.

Greenland is under NATO's protection, they say, and any forceful attempt to take it would break the alliance.

Arctic and Greenland expert Mika Blujan-Mared says it's hard to predict what Trump will do, but territorial expansion to mark America's 250th anniversary this year is the kind of thing that would appeal to the president.

Delivering the massive, mineral-rich island would bring an additional 25% to the landmass of the U.S., he says, and make it the world's second largest country after Russia.

Eleanor Beardsley, NPR News, Paris.