Michael Ellman from University of Amsterdam says about the Dutch election that"The main loser is the traditional Social Democratic party, the Labour Party or from its Dutch initials PvdA. This party has played a major role in Dutch politics since 1945 but fared dismally in these elections. I think the main reason is that it was the junior partner in the coalition and went along with fiscal orthodoxy/austerity which hit many of its traditional voters who turned elsewhere to express their dissatisfaction. For many years now it has been a 'New Labour' type of party and not a home for victims of globalisation. This has not pleased many of its traditional voters. It is also a culturally liberal party which also did not go down well with many of its traditional voters."
That does not mean that an extreme left answer is the best strategy, as shown in this article by Zack Beauchamp. This autor argues that left or center left parties that focus on redistribution have a hard time convincing voters that do not want to share their welfare with "others". That probably requires some convincing that more and more, in our integrated world with huge global challenges, "us" also includes "others."
Applied to the U.S., it means that
"The uncomfortable truth is that America’s lack of a European-style welfare state hurts a lot of white Americans. But a large number of white voters believe that social spending programs mostly benefit nonwhites. As such, they oppose them with far more fervor than any similar voting bloc in Europe.
In this context, tacking to the left on economics won't give Democrats a silver bullet to use against the racial resentment powering Trump's success. It could actually wind up giving Trump an even bigger gun. If Democrats really want to stop right-wing populists like Trump, they need a strategy that blunts the true drivers of their appeal — and that means focusing on more than economics."