After 1865, america was dominated by northern European Protestants voting Republican, while the democrats were an alliance of southern bigots and northern religious minorities, Catholics and
Jews, unified only by their opposition to the majority. So from that day to this, democrats have seen themselves as the opposition party encouraging immigration as the road to power. in 1965 democrats enacted a law ending the quota system which gave a big preference to northern Europeans. Later the diversity immigration visa program was enacted to give a preference to nationalities which had few immigrants in the past. Then democrats have resisted all attempts to limit abortion and keep trying to pay for it. About 70 million Americans have been aborted, to be replaced by immigrants.
Clinton gave a famous speech at Portland University extolling immigration for diversity.
http://www.presidency.ucsb.edu/ws/?pid=56140
In another speech he said it would be a good thing when there was not white majority.
Obama has pursued immigration as his number one priority, illegal giving amnesty to 12 million illegal invaders, and otherwise doing everything he can to increase immigration.
In a recent speech he explained that immigration is good because "diversity" will help the US find a "common purpose", i.e. democrat, liberal ,socialist