I generally think that the national Democratic Party should stay out of primary races and let the democratic voters decide who should be on the ticket for the party, but this is the one scenario when I think the national party needs to step in. It is definitely in the party's interest to assure that a democrat is on the ballot in the November election. It isn't interfering with the primary process when there is a serious possibility that the Democrats, while easily outnumbering Republicans in the District, might be shut out entirely.
That said, I don't know if the national party can make a difference. Ideally, they could get one of the front-running dems to withdraw, maybe by giving him a job in the national organization or with help supporting him in a future campaign. But the latter would open the party up to a charge that it is interfering in that future campaign where interference might not be a warranted as it is now.
I guess the moral of this story is jungle primaries are a bad idea. They give a major advantage to incumbents and are a process that looks more democratic on paper but will tend to produce a result that is less representative of the district. But if there are jungle primaries, the national party is justified to do what it can to make sure it doesn't screw democrats.
