Trump’s immigration crackdown is stressing out deployed US troops

Does anyone here think this is really an issue within the military? I read the article and it appears the author is discussing "illegal immigration" yet keeps citing sources only about "immigration". Even citing the source inaccurately it seems:
"Of the 18.8 military veterans nationwide, more than 1.5 million were born in the U.S. with a parent who was an immigrant, according to an analysis by the Migration Policy Institute."
How can there only be 18.8 military veterans nationwide?