Yes, DACA.

Yes, this is a litmus test for Democrats on immigration issues in the coming primary season.

Primary litmus-tests don't select for candidate who will do very well in the general elections. It's been true for the Republicans, and it's been true for the Democrats.

The only time they work is when applied consistently over decades, the way "NO NEW TAXES" has been, and "DON'T TAKE OUR GUNS." This is not one of those issues yet. Maybe in the 2030 election.