The evidence for me lays in the states of Minnesota and Michigan. In states like New York and California, they have successfully captured the legislature. The democratic party doesn't do shit in those states and seems to be regressing.

However, MN is a solid purple state despite their voting record, and MI has been contested back and forth for decades. Both states got a democratic majority in all branches of government, and they both got hard at work passing year's worth of progressive policies in the last year. In typical liberal fashion they only went after policies that had a supermajority of support, but they likely succeeded in securing the next election because of it.