This detachment could also make him a withholding boss who dispensed few thanks or apologies. “His reputation for staying calm made even the mildest verbal slight or passing glance sting all the more,” Mr. Alter writes. He adds that aides “often knew Obama was satisfied only when he said ‘What’s next?’ ” and that some “came to fear Obama’s dropped smile, his way of beaming broadly and insincerely before reverting instantly to a frown and a penetrating glare.”

Mr. Alter emphasizes that Mr. Obama was “virtually the only one in his inner circle” who wanted to go for a big health care program in his first year; many staff members, he says, worried that such “a big reform package would overload the circuits” and argued that he should focus on the economy or energy instead. Mr. Alter adds that health care was not high on Mr. Obama’s initial to-do list either: an internal memo from his Senate office, he points out, “showed that as recently as 2006 he had listed his policy priorities in the Senate as energy, education and nonproliferation; there was no mention of health care.”

Why did Mr. Obama’s thinking change? As Mr. Alter recounts it, Mr. Obama told his aides that “in a quiet moment on Election Night he had asked himself, ‘What’s the single achievement that would most help average Americans?’ ” and that his answer “was health care reform, though he hadn’t emphasized it during the campaign.” As president, Mr. Alter goes on, Mr. Obama pressed on “because for greatness he needed health care” and “because he was genuinely convinced that the status quo was financially unsustainable” given rising health care costs.

On Afghanistan, Mr. Alter writes, the president came “into office knowing little about the situation on the ground” there and “received advice from Bush holdovers that he wasn’t prepared to resist.” As a result, “he stumbled into a large commitment without fully realizing what he was getting into,” and “when he saw what had happened, he slowed everything down in August and September and launched the most detailed presidential review of a national security decision since the 1962 Cuban Missile Crisis.”

Although the Pentagon tried to take advantage of the new president’s inexperience in running a huge bureaucracy and box him into supporting Gen. Stanley A. McChrystal’s recommendations, Mr. Alter says, the president summoned Mr. Gates and Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, to the Oval Office in early October, telling them that leaks and positioning in advance of a decision were “disrespectful of the process.” In what Mr. Alter describes as “a cold fury” and as “the most direct assertion of presidential authority over the U.S. military since President Truman fired General MacArthur in 1951,” Mr. Obama demanded to know “here and now” if the Pentagon would be on board with any presidential decision and could faithfully implement it.

In this volume Mr. Alter is toughest on what he sees as the narrow approach of the White House’s economic team in dealing with Wall Street. He says that, as one former Treasury official observed, the president’s economics team, headed by Mr. Geithner and Lawrence H. Summers, “ran the gamut from A to C,” , and that more progressive voices who had advised the campaign, like Robert Reich and Joseph Stiglitz, were increasingly marginalized.