After years of scandal and remediation at Fannie Mae and Freddie Mac, and hearings and legislation on Capitol Hill, have GSE reform advocates finally decided to press ahead with a measure as the congressional calendar winds down? Some GSE observers think so, and they cite a few recent developments to back up their assertion. Earlier this month, in an unusual challenge, 20 Republican senators sent a letter to Senate Majority Leader William Frist, R-TN, and…