It’s not even really a secret, and it’s not just about voting.  We know that there are millions of them, especially in important election states like California.  The issue is about representation in Congress and the electoral college.  Right now, we count illegals along with citizens when it comes to overall population numbers; the illegal population is counted towards a state’s electoral college numbers etc.  This boosts the state’s population artificially.  Illegals don’t even have to be actively voting to be beneficial.