What is a 'national emergency,' and how can Trump use it to fund border wall?

President Trump is hoping to avoid another lengthy government shutdown over funding for a border wall, vowing to sign a border security compromise package and declare a "national emergency" to complete his oft-repeated campaign promise. Trump has repeatedly demanded more than $5 billion for a wall along the U.S.-Mexico border. When he campaigned for president, he often promised Mexico would pay for the wall. Democrats have refused to capitulate to Trump's budget demands, and House Speaker Nancy Pelosi has rejected what she calls an "immoral and hateful obession" with building a border wall. -- MORE...