With the GOP going completely off the rails the easiest path to victory is to simply go middle of the road and pick up all those independents/centrists and conservatives with brains.

I think we may have found out that's a risky strategy in the general election in 2016. It's as if having a choice between a status quo centrist and republican crazies isn't good for turnout- when the American Dream is increasingly regarded to be a cruel joke by young voters and the result is such low turnout that if 'did not vote' had been a candidate it would have won, maybe it's time for the Dems do some soul searching here.

I don’t see him suddenly switching to anything resembling a “strong progressive agenda” because it will just give his GOP opponent ammo to claim “see he’s radical too”.

I don't see him switching either, and in any case it doesn't make sense for him to run away from progressives to avoid being called radical- after all, they're calling him radical anyhow and it's unlikely they'd stop doing that

To the extent that running to 'the center' is seen as just appeasing Republicans in trade for no benefit to anyone but those Republicans (I think it is seen that way by a lot of younger, left and independent voters), I take the view that the one thing the Democrats must do (if they do nothing else) is keep on pressing hard on antitrust enforcement and restoring unions and labor protections and promoting environmental protection. If they don't, I expect a lot of stupid protest votes going to the green party or other splitter factions set there to split the democrats and lower the bar enough for the GOP to heave a fascist boomer into the white house where they will finish the job of dismantling American democracy