A group of migrants made up mostly children and women have been traveling through central America and Mexico organized by Pueblo Sin Fronteras, a migrant rights group.

President Donald Trump has been following the migrants’ progress with a series of tweets, finally announcing, and confirmed by Homeland Security Secretary Kirstjen Nielsen, that the U.S. would be deploying the National Guard to the U.S.-Mexico border.

Details of the deployment are still, in many cases, unclear — such as how long the National Guard will be deployed, where along the border they will actually be, how many troops will be needed.

But even without those numbers, we can take a look at previous National Guard deployments to get an idea of past effectiveness, cost, and time frames.

The Show talked with Michel Marizco, Fronteras Desk senior editor, for more on the topic.