The issue of whether we include illegal aliens for apportionment purposes goes to the heart of our sovereignty. Who do our elected "representatives" represent? Who is "We the People?"
In addition to the President's executive order, there is pending litigation out of AL on this very issue. I suspect the SCOTUS will have to decide this issue, along with several other questions that concern our sovereignty. At the end of the day, the Court basically has a choice—exclude illegal aliens from apportionment, or concede that the Constitution is fatally flawed in that it politically empowers non-citizens at the expense of citizens' political representation. The USA will not survive long if the Court chooses the latter course.