A Senate bill to overhaul the U.S. mortgage-finance system would devote billions of dollars to boosting home ownership among lower-income borrowers, according to a recent draft obtained by Bloomberg News. The draft, the result of discussions between Sens. Bob Corker (R-Tenn.) and Mark Warner (D-Va.) gives the clearest view yet into how the senators aim to woo progressive politicians to back their plan for addressing mortgage-giants Fannie Mae and Freddie Mac. Support from those Democrats is likely needed to meet the 60-vote threshold for passing major bills in the Senate. Corker and Warner would levy a “market access fee” on new loans. That money would be used to help build affordable-rental housing and make buying homes cheaper for low- and moderate-income borrowers, according to the draft.