Freddie Mac is touting a new affordable-housing program that it says will help lenders reach more credit-impaired borrowers. But the program could be scrutinized by the Bush administration, which is flexing its muscle with a pledge to review new GSE endeavors for charter and legal compliance. Dubbed “Home Possible,” the program will allow borrowers to obtain up to 100 percent financing with a $500 downpayment, if they are below the median income and…