At least a third of landowners approached by state officials have refused to let wall be built on their properties, leaving sections full of gaps.

WASHINGTON - Newly sworn-in U.S. President Donald Trump said on Monday that he would declare illegal immigration a national emergency, send troops to the U.S.-Mexico border, and reinstate his "remain in Mexico" policy as part of a sweeping immigration crackdown.

The speech underscored President Trump's continued focus on immigration, which he called the nation's "number one issue."