The only state that Clinton won that seems vulnerable is New Hampshire. In 2018, NH was split with Republicans retaining the Governor's mansion and Democrats taking the state legislature and both US House seats.
Michigan and Pennsylvania are likely back in the Democrat column. The most telling exit poll question was whether sexual harassment was more or less of a issue in this country. In both states, the number who said it was more of a problem was over 50%. Female voters buried Republicans. Wisconsin was a win for Democrats as they narrowly won the Governor's race and won several more statewide offices easily. Also Foxconn could be a issue that works against Republicans as the Republicans passed a bill to stop a Democrat Governor from ending the deal and with the Foxconn mess, the state could be on the hook for billions even if they break their promise which it seem they are.
Republicans could also have major issues among other states Trump won. Republicans had to pull every dirty trick to prevent people from voting to eke out a narrow win in Georgia's Governor's race. In Arizona, Democrats won 3 statewide races marking the first time any Democrat has won statewide. If Biden is the nominee, Texas could take the route of the Texas Senate race in 2018. A narrow Republican lead. In Maine, Republicans are likely to lose the lone electoral vote they won because of the tiered voting system they use in federal elections.