It was a reasonable retort considering the attack on him by the "Gang of Four" (I'm giving them a new handle).
Racism is never reasonable.
It is never, ever, acceptable to tell a citizen of your own country to go back to where they came from (as if they are a foreigner and don't belong). Obviously Trump's criteria on whether a person belongs to USA or not is based on skin colour/race rather than citizenship or birthplace. That's racism, right?
This is such a cliched phrase from bigots and racists.
Non bigots and non racists never say this phrase.
Think about it.
Have you ever said this phrase to someone who is a citizen of your country?
Would you ever say this phrase to someone who is a citizen of your country?
Would you say this to a white person who is a citizen of your country?
Would you say this to a person who is a minority ethnicity and a citizen of your country?
Is this acceptable behaviour from your president?
Do you want to encourage this behaviour in your society?
Are you going to start behaving this way?
Are you going to encourage your children to behave this way?