I don't know who he is: Trump on Greenland Premier who said 'We choose Denmark'

US President Donald Trump said he doesn't know who is the Premier of Greenland. This comes after Premier Jens-Frederik Nielsen said people of Greenland choose Denmark over US. When asked about this, Trump said, "I don't know anything about him. But [choosing Denmark] is gonna be a big problem for him." Trump wants to acquire Greenland for national security reasons.