Social democrats believe that the Democratic Party has to be rejected outright or transformed into a social democratic institution. Go for it if you think you can do it, but I fear that the capitalist class will never again allow the non-rich to increase their share of the wealth, in America or any other Western country -- at least not without literal bloodshed. I don't think it can happen through democratic means anymore (though I hope it can). With few exceptions, candidates can't get elected without the kind of money only these plutocrats can provide. So of course the economic order can't be seriously transformed. Democrats can't do it and social democrats won't be able to either, because they won't be able to raise enough money to win the number of elections they'd need to win to make serious change.
This morning Bloomberg told us what corporations are doing with their GOP tax cuts. Surprise: the cuts aren't trickling down to workers. The fat cats are holding on to them.

I'm looking at Italy's elections and seeing a pro-Putin nationalist party winning the most votes. And even as it appears that we in America are pushing back on a fascism-curious president, I worry that what's happening in Italy is every Western country's likely fate: The capitalists insist that less and less money should flow to the non-rich, the non-rich can't get what they want even when they vote progressive, so in every country they're eventually going to take out their frustrations on non-whites and immigrants, and racist nationalists will inevitably rise to power sooner or later.
Maybe in the long run the capitalists will suffer as well from this world order they've created -- or maybe not. Right now I fear that they're the only ones who could turn this around, by accepting a reallocation of wealth, something I can't imagine them doing. Despite my pessimism, I continue voting Democratic, because slowing the flow of money in the direction of the rich still seems worthwhile, as does the expansion of rights for previously disfavored groups, which the rich don't seem to mind, and Republicans do. Perhaps I'm underestimating the possibility of serious positive change. I hope so.