Trump wants up to 15,000 troops at border to deal with migrant caravan. Political stunt or national emergency?

In order to fire up his base, President Trump wants to deploy up to 15,000 troops to carry on his political stunt at the US-Mexican border.

For context: The United States currently has 14,000 troops in Afghanistan. There are 5,200 in Iraq and about 2,000 in Syria.