Now Trump wants to send National Guard troops to the Mexican border

https://www.huffingtonpost.com/entry/trump-national-guard-border_us_5ac52858e4b0aacd15b7f439
Isn’t there a constitution prohibition against using US troops inside the borders?

There's constitutional prohibitions against quite a few things Trump does. Hasn't made a difference so far.

I don't know if the Constitution prohibits the use of the National Guard. Happens all the time at state level. Happened at Kent State with the Ohio National Guard.

Posse Comitatus Act

Quote :

The Act only specifically applies to the United States Army and, as amended in 1956, the United States Air Force. While the Act does not explicitly mention the United States Navy and the United States Marine Corps, the Department of the Navy has prescribed regulations that are generally construed to give the Act force with respect to those services as well. The Act does not apply to the Army National Guard or the Air National Guard under state authority from acting in a law enforcement capacity within its home state or in an adjacent state if invited by that state's governor. The United States Coast Guard, which operates under the Department of Homeland Security, is not covered by the Posse Comitatus Act either, primarily because although the Coast Guard is an armed service, it also has both a maritime law enforcement mission and a federal regulatory agency mission.

"Posse Comitatus". Sounds familiar.
Wasn't he the drummer for the Miami Sound Machine?