Immigration isn't good for wages period. Especially if you migrate to the US where you get on welfare and you have kids and your kids go to school for free and you don't pay tax, you actually cost the country more than the natives.
It's only good for the rich (to give lower salaries) and the democratic party memebers who were hoping to accelerate migrants path to citizenship so they vote for them in return. I truly believe if Hillary won this election, republicans wouldn't have been able to win in the future at all. You've seen how the winner in key states was only few points ahead and having more latinos, Muslims etc voting would ensure the dems stayed in power.
As for the DNC, they have to do what's best for the people now and take on issues that are affecting the lower/middle class or they will not win. Hillary's plan to brown america failed, so they have no choice but to fight for the lower and middle class votes. One of the ways to fight for their votes is to oppose Immigration. (the wages will go up naturally because you decrease supply -> increasing demand)