There is a little-discussed aspect of illegal immigration which will have an increasing impact on the political composition of Congress. Not only is a state's congressional representation based on the number of persons within its borders, but each congressional district is apportioned the same way. This means that congressional districts must contain the same number of persons but not the same number of voters.
As a result, a district packed with illegal aliens requires fewer votes to win an election majority. Since these persons tend to congregate in poorer districts, this allows Democrats to spread their voters over other districts in order to win those elections as well. (After all, a 51% majority in an election is just as good as an 80% majority.) This also allows Democrats in low-voter districts to spend less on their own campaigns and give the money they have raised to other Democrats' campaigns. No wonder we have had such unrepresentative Congresses.*
The US Constitution only used the term "person" because there was no such thing a "citizen" at the time of its adoption. Unfortunately, this historically transitional term has been transmuted into a permanent fixture of Congressional apportionment. Since SCOTUS has been unwilling to address this confabulation, it seems that a federal law, If not a Constitutional Amendment, is needed to correct this situation. But I am not holding my breath.
*This is not exclusively limited to Democrats, but their predominate contribution to this problem precludes any moral equivalence argument.