Yes, they can protect our border. This article was from CNN and should have had a barf alert - my bad.
Many have posted good information on this thread about what can and cannot be done by our troops.
By the way, this statement is directly from the White House email:
“Homeland Security Secretary Kirstjen Nielsen said the migrant caravan headed for the U.S. southern border will not cross over into the United States, on ‘Fox News Sunday,’” Nick Givas writes in The Daily Caller. “There is a legal way to enter this country. Those who choose to enter illegally will be stopped,” Secretary Nielsen said.”
I gave the article some merit because on Fox last Friday there was an “expert” from law enforcement who said something similar. He said only law enforcement could act on the border and it was unconstitutional for the army to have a role there.