Hasen on Costa on Giuiliani:

Let me spell this out a bit more. The rules under the Electoral Count Act are complicated and some are not clear, but this much is clear: you don’t go to a contingent election (where each state delegation gets only one vote) unless no candidate gets a majority. That won’t happen if a state sends in two slates of electors: one through the normal process as certified by the governor and one from some rogue state legislature. In that circumstance, the ECA provides that the governor’s slate of electors prevails. In Michigan, Pennsylvania, and Wisconsin, there are Democratic governors. Those governors would send in slates that would prevail.