Is saying "go back to where you came from" racist?

Trump's recent tweet suggesting that "progressive Democrat Congresswomen" (which many believe is referring to Rep. Ocasio-Cortez, Rep. Omar, Rep. Pressley and Rep. Tlaib, aka The Squad) go back to where they came from has caused an uproar from the Left who believe it is more evidence of his racism.  But is his tweet actually racist?  Is the word 'racism' overused?  What is the difference between explicit and implicit racism or other biases?  And ultimately what does this latest political controversy mean for the 2020 election?   References (links may only work on www.redmombluemom.com): Axios poll (July 2019)   Rasmussen poll (July 2019)   Trump's comments on Charlottesville - transcript (LA Times, Aug 2017)   Trump is leading a hate movement (Washington Post, July 2019) *behind paywall*   16 examples of Trump being racist (HuffPost, Feb 2017)   The President strikes back (Power Line Blog, July 2019)   Dissent can be patriotic, hating your country isn't (The Federalist, July 2019)