Denmark’s prime minister Mette Frederiksen has warned that U.S. President Donald Trump is serious about taking over Greenland, adding that a U.S. attack on a NATO ally would be the end of all, with concern in Copenhagen renewed after Washington’s recent actions against Venezuela hardened views on Trump’s use of power. "If the United States decides to militarily attack another NATO country, then everything would stop -- that includes NATO and therefore post-World War II security," Mette Frederiksen told Danish television network…