President Obama held a  news conference at the White House , fielding questions  on  the budget & deficit,  military involvement in Libya and the War Powers Act.. John Chambers the chairman of S&P's sovereign ratings committee, said on Tuesday that U.S. Treasury bills maturing on August 4 would be rated 'D' if the government fails to honor them. Unaffected Treasuries would be downgraded as well, but not as sharply, he said. "If the U.S. government misses a payment, it goes to D," Chambers said. "That would happen right after August 4, when the bills mature, because they don't have a grace period."