Mexican Gunman Fires Across Border Toward U.S. Highway Workers

Our border security issues continue to pile up.  It was just reported that in the border town of Quitman, Texas some highway workers were shot at - from Mexico - with high powered rifles.  What is the US response to this? 
It would appear that the same offense (that is an act of war between North and South Korea) is really no big deal along the US - Mexican border.  Why would the federal government want to secure the border when they have freedom of speech and political rhetoric to limit?