The Standard & Poor's credit-rating downgrades of mortgage giants Fannie Mae and Freddie Mac are not very surprising, Sen. Jim DeMint (R-S.C.) said.

"Fannie & Freddie downgrade isn’t surprising, they've relied on over $160 billion in endless taxpayer bailouts," DeMint tweeted on Monday.

"Time to break up the mortgage giants & privatize them. Forcing taxpayers to prop them up hasn’t solved crisis; it has prolonged it," DeMint continued in a follow-up tweet.

Earlier on Monday, S&P downgraded the government-sponsored mortgage companies' credit ratings from AAA to AA+. That downgrade came after the ratings agency made the same reduction to the U.S. on Friday.

S&P said the downgrade was because of the agencies' reliance on the U.S. government.

"Their ability to fund operations relies heavily on the U.S. government," S&P said.

In 2008 the federal government took over Fannie Mae and Freddie Mac as the subprime housing mortgage market started to collapse.