President Donald Trump speaks to reporters as he visits the banks of the Rio Grande River with Senator John Cornyn (R-TX), Senator Ted Cruz (R-TX) and U.S. Customs and Border Patrol agents during the president's visit to the U.S. - Mexico border in Mission, Texas, U.S., January 10, 2019. Flanked by border agents who are going without paychecks during a government shutdown, U.S. President Donald Trump threatened on Thursday to use emergency powers to bypass Congress to pay for a wall on the U.S.-Mexico border. REUTERS/Leah Millis

President Donald Trump shakes hands with U.S. Border Patrol Air and Marine Operations Director Don Sperling as he visits the banks of the Rio Grande River with Senator Ted Cruz (R-TX) during the president's visit to the U.S. - Mexico border in Mission, Texas, U.S., January 10, 2019. Trump flew to the Texas border with Mexico to try to bolster his case for the border wall as a partial U.S. government shutdown tied to the issue stretched into its 20th day with no sign of new talks to resolve the impasse. REUTERS/Leah Millis

President Donald Trump speaks with a U.S. Customs and Border Patrol agent as he visits the banks of the Rio Grande River with Department of Homeland Security Secretary Kirstjen Nielsen during the president's visit to the U.S. - Mexico border in Mission, Texas, U.S., January 10, 2019. "We can declare a national emergency. We shouldn't have to," Trump told reporters. "This is just common sense." REUTERS/Leah Millis

President Donald Trump talks with U.S. Border Patrol agents as he attends a roundtable discussion at the U.S. Border Patrol Station near the U.S. - Mexico border in McAllen, Texas, U.S., January 10, 2019. Such a step would likely prompt an immediate legal challenge over constitutional powers from congressional Democrats - a challenge Trump said he would win. REUTERS/Leah Millis

U.S. President Donald Trump greets U.S. Border Patrol agents standing with their all terrain vehicles, motorcycles and a boat on the banks of the Rio Grande River during his visit to the U.S. - Mexico border in Mission, Texas, U.S., January 10, 2019. The Republican president is adamant that a government funding bill to end the shutdown include $5.7 billion for a border barrier - his signature campaign promise. Congressional Democrats oppose that. REUTERS/Leah Millis

President Donald Trump salutes a U.S. Border Patrol helicopter with U.S. Border Patrol agents as it flies over the Rio Grande River during his visit to the U.S. - Mexico border in Mission, Texas, U.S., January 10, 2019. The standoff has left a quarter of the federal government closed down and hundreds of thousands of federal employees without pay. REUTERS/Leah Millis