Nevada will probably fall out of easy reach for Republicans after 2020 (it's still one of Trump's first possible flips). People sometimes say Idaho, but by the time that happens the trends will have reversed and party coalitions will have changed. Another fracking boom could do this fast in the Dakotas. Any migration to Wyoming will have an impact because there's only half a million people there.
If the Bakken were closer to Fargo, I could see this as a possibility many, many years down the line. Not because extraction workers are left-leaning (quite the opposite), but as a second-order consequence of ND's dominant metro becoming denser and more populous. However, the Bakken sits at the opposite end of the state, so the primary effect of a second boom would be to boost the populations of towns like Williston and Dickinson into the ~30K range. Which I can't imagine being much of a boon to the D-NPL.
