Republican and Democrat lawmakers in the Senate formally unveiled their ambitious plan to replace Fannie Mae and Freddie Mac with a new federal entity providing backstop guaranties for securities backed by high-quality conventional mortgages. Although they made a variety of changes to a “discussion draft” version of the legislation that has been widely circulated in recent weeks, the proposal still faces a huge hurdle in the House despite winning generally favorable reactions from industry groups. As it was introduced this week, S. 1217, the Housing Finance Reform and Taxpayer Protection Act of 2013, would create...