As per the 14th Amendment of the US Constitution, All those born or naturalized in the United States are citizens of the United States and of the State wherein they reside.
Ending Birthright Citizenship was one of the promises of Donald Trump during his 2016 Presidential Campaign. He wishes to keep his promise by the time 2020 Presidential Elections gonna happen.
Non-Citizens may no more have the luxury of gifting US Citizenship to their babies soon after the birth. It's gonna be a big factor in the next Presidential Elections.