The heavyweight Wall Street group that sets the to-be-announced MBS standard is pushing federal regulators to take aggressive steps to keep Fannie Mae and Freddie Mac programs aligned as much as possible as the government-sponsored enterprises develop a new single security. In a sternly written letter to the GSE regulator, the Securities Industry and Financial Markets Association warned that the TBA market could be disrupted if Fannie and Freddie policies diverge too much under the new system in which the GSEs would issue fully-fungible securities. “If performance and credit risk are not aligned, then the securities will not be fungible and the market will not trade them as if they are,” the group said. SIFMA argues...