Fannie Mae and Freddie Mac could continue to operate even if the U.S. debt ceiling is not raised by Aug. 2. But raising the ceiling alone, without a budget deal, would leave them — and a mortgage market that relies on their guarantees — vulnerable.Despite improvements in their financial results, the government-sponsored enterprises need continued capital injections from the Treasury Department to avoid being unwound by their conservator, the Federal Housing Finance Agency (FHFA), according to the rating agency Fitch Ratings. On average, the GSEs have been drawing $2 billion to $3 billion a quarter since 2010, said analysts at Barclays Capital.

"Fannie and Freddie right now given some legacy portfolio issues are likely to need ongoing support from the government," says James Moss, a Fitch analyst. "That flexibility is going to be compromised or lost if they don't raise the debt ceiling."

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