The only word from the incoming Trump administration about the fate of Fannie Mae and Freddie Mac is that the prospective Treasury secretary wants to bring them out of conservatorship. The Obama administration, however, commits only to preserving an explicit government guarantee for a “defined class” of MBS. “The explicit government guarantee would be funded by financial institutions and would act as insurance against catastrophic losses,” said the Treasury in a late December blog posting by Jane Dokko, deputy assistant secretary for financial economics, and Sam Valverde, a counselor in the Office of Domestic Finance. However, the authors don’t elaborate on what would shape the defined class. Under the new guarantee, investors would be assured...