The dems legalize 10 million illegals. They become citizens. Citizens vote. (Don't be fooled, the Democrats aren't doing this out of the goodness of their hearts. They're buying voters.)
Then chain migration kicks in and 10 million becomes 30 million.
Meanwhile the census counts every one of them in LA, New York, Chicago, and every other sanctuary hub, which equals more House seats, which means more electoral votes.
Then they pack the Court, kill the filibuster, add DC and Puerto Rico, and it's over. Elections still happen, they just don't mean anything anymore.
Et voilà! A one-party state.