He promised to put an end to the Bush economic disaster and the wars in Afghanistan and Iraq and to pass universal health care, completing a Democratic dream dating back at least to F.D.R. The most populist idea Mr. Obama offered was his vow to repeal the Bush-era tax cuts for the rich, while keeping them in place for the middle class.

After Mrs. Clinton won the New Hampshire primary in 2008, Mr. Obama responded with an intonation crafted in defeat, which was designed to stir not revolutionary fervor, but patriotic hope; proclaiming that it was “written into the founding documents” of a flawed but earnest nation yearning to perfect its union: “Yes, we can.”

Mr. Obama was arguing for his own electability as a black man in a country that had never elected anything but a white man as president.

Candidate Obama didn’t favor overturning the country’s private health care system or even instituting the individual mandate to purchase health insurance that Senator Clinton insisted was necessary to extend coverage, though he later adopted it as president. And Mr. Obama vehemently fought the notion that he was a socialist, or even out of the ideological mainstream. He ran as a centrist and a national healer, clearly not knowing that he would face an opposition once in office that was equal parts trenchant and ideologically radical.

Once elected, Mr. Obama faced immediate and continual fire from vocal contingents on the right, but also from influential left-wing bloggers and liberal and libertarian radio hosts whom the White House press secretary Robert Gibbs derided in 2010 as “the professional left.”

Some of these figures have dined out on the theme that Mr. Obama promised them a revolution and sold out instead to the establishment and the big banks. The liberal TV and radio veteran and longtime columnist Bill Press has even written a book on the theme, “Buyer’s Remorse: How Obama Let Progressives Down,” for which Mr. Sanders provided a blurb.

But many African-Americans chafed at the fact that these mostly white liberals had hardly given the new, and first black, president — with all the unique historic challenges the latter fact entailed — time to tackle the sinking economy and get health care through before demanding that he issue executive orders defying the “don’t ask, don’t tell” law and somehow unilaterally close the Guantánamo Bay prison without the consent of Congress. Mr. Obama and his attorney general, Eric H. Holder Jr., were excoriated for failing to jail Wall Street bankers whose rapaciousness triggered the Great Recession.