Howard Kurtz has a nice piece on last week's attack of Rep. John Murtha (D-PA) on the House floor by Rep. Jean Schmidt (R-OH): "It is an age-old device in politics, making a personal slam sound more high-minded by attributing it to someone else."
Typical formulations:
"There are those who say that Congressman X is a gutless wonder."
"I was talking to someone just the other day who questioned whether Congressman X is a gutless wonder."
"Now I don't agree with those who say Congressman X is a gutless wonder, but he does owe us some answers."
Of course, it's much less effective if the person you're quoting never even said it.