Some Inside Baseball on US Democrat strategy:
With that said, there are more costs to Democratic weakness in the states than just House elections. States are where parties build talent and try new ideas. Here, the GOP is instructive. Its brightest stars are either governors (Scott Walker, John Kasich, and Chris Christie) or former state officeholders (Marco Rubio, Ted Cruz, and Joni Ernst). And Republican-controlled statehouses have been incubators for conservative ideas...
...Only a few places stand as incubators for progressive strategies and ideas, and nationwide, Democrats have close to nothing in the way of a bench for federal and statewide office. The liberal counterparts to Walker, Christie, Brownback, and Mike Pence—ideologically motivated governors with national profiles—don’t exist. And as a result, liberals can’t point to a forward-looking agenda that exists outside the bounds of the presidency.