Could excluding non-citizens from census results change the number of House members apportioned to some states?
Excluding non-citizen residents from the usual basis for allocating Congressional seats could change the size of some state delegations. A recent Presidential statement calls for excluding undocumented residents "to the maximum extent feasible." They have previously been included for both apportionment and certain funding formulas. The decennial census, still underway, counts all U.S. inhabitants, plus federal employees overseas.
Each state gets one seat in the House of Representatives, with the remainder allocated by population. The Center for Immigration Studies, which favors less immigration, says California, Florida and Texas could each lose a seat under such a change, with Alabama, Minnesota and Ohio picking up one. The exact result would depend on the method for adjusting census estimates, assuming Trump is re-elected and courts permit the change.