Four military police units from Texas are among as many as 1,500 active-duty troops bound for the nation’s southern border to “bolster security,” military leaders said Friday.

President Trump is sending hundreds of troops to the southern border for a wide-ranging mission that poses new challenges and raises questions about the military’s role in handling migration, traditionally a law enforcement responsibility.

As active-duty U.S. soldiers began moving toward the nation's southern border to confront what President Donald Trump called "a national emergency," much is still unclear about their mission, including whether they would be armed,