Senator Mitch McConnell of Kentucky, the Republican leader, is often assailed by Democrats for blocking the Democratic agenda. He said the results absolved him of that charge.

“I am amused with their comments about obstructionism,” Mr. McConnell said in an interview. “I wish we had been able to obstruct more. They were able to get the health care bill through. They were able to get the stimulus through. They were able to get the financial reform through. These were all major pieces of legislation, and if I would have had enough votes to stop them, I would have.”

Mr. McConnell said, though, that the Democratic victories would come at a price, predicting that the party’s decision to push sweeping measures in the face of public opposition smacked of arrogance and “is sowing the seeds of their potential downfall.”

It is true that Democrats are struggling to translate their accomplishments into popular support, and the difficulty of doing so is perplexing them.

During a luncheon in early August with select Democratic senators in the Roosevelt Room at the White House, President Obama gave voice to that sentiment. He told his guests, according to lawmakers, that Democrats were winning and that critics within the party were wrongly focused on “what didn’t happen rather than what we have accomplished.”

Democrats offer several rationales for why they are not breaking through with their legislative successes. They note that some of the chief benefits of the health care law and the overhaul of the financial industry, for instance, will not be felt for years. And they say that a news media environment that thrives on conflict makes it harder to get out their message about constructive achievements. Most important, they say, difficult economic times produce a disgruntled public.