Barack Hussein Obama has now been president for six months - when campaigning he avoided using his full name, now he embraces it. As he passes this half-year milestone, his honeymoon with the public may be ending - although America's media remain gaga over him. Obama is readying for a major fight over health care. His popularity is starting to sag. As he enters what was a difficult phase for new presidents, Obama should learn from history not to bank only on his charisma. Other presidents have learned the hard way that depending too much on personal magic can prove tragic for the country. Thus far, simply getting elected has been Obama's greatest achievement. On Election Day, and with his inauguration, Barack Obama brought hope to a depressed country. Counterfactuals are impossible to prove, but it is hard to believe that electing John McCain or Hillary Rodham Clinton would have generated the excitement of Obama's victory. A McCain win in particular probably would have triggered rounds of recriminations and accusations of racism, especially considering most reporters' pro-Obama bias during the campaign - and since. Obama played his part magnificently. "Yes We Can" inspired a country demoralized by George W. Bush's lethargy, Iraq's complexity, New Orleans' devastation and the financial collapse. As both candidate and rookie president, Obama demonstrated perfect political pitch on the racial issue, never indulging in racial demagoguery or anger, refusing to run as the black candidate, but embracing his historic role as an agent of healing and change when he won. GOVERNING, of course, requires more than winning election by spinning an uplifting personal narrative. In fairness to Obama, when he started running he - and most everyone else - believed these years would be times of continued prosperity. Few anticipated the financial crash, although that secured Obama's victory, given that the debacle occurred on the Republicans' watch. Obama has also been blessed by his predecessor's unpopularity and the Republican opposition's stunning impotence. But Obama has been cursed by this financial crisis's depth and complexity. So far, he has blamed Bush. But, as Ronald Reagan learned, presidential success early on - and pie-in-the-sky promises about saving the economy - quickly make the incumbent responsible. In 1981, Reagan blamed Jimmy Carter and the Democrats for the great inflation, high interest rates and crushing budget deficits he inherited. After many legislative successes and hope-laden speeches that culminated in August 1981, seven months into his presidency, the economy nose-dived. When Congress returned from its summer recess, Democrats blamed their constituents' suffering on "The Reagan Recession." The $787 billion stimulus plan could end up being Obama's albatross. He erred by allowing the congressional pork-kings to dictate the legislation, burdening it with pet projects rather than smart stimuli. He further erred by forgetting his vows of bipartisanship and post-partisanship, thus failing to share responsibility with the Republicans. ULTIMATELY, like Reagan, Obama has time on his side. All he needs is a recovery by spring 2012 and he can still claim a new, Reaganesque, "morning in America," with his own liberal twist. But by veering as far left as he has domestically, by playing the hard partisan game he has, he risks following in the footsteps of Jimmy Carter - who six months into his presidency scored about 10 percentage points higher than Obama has in public approval surveys. And Obama is now entering a particularly difficult passage in his presidency as he tries to overcome the health care reform curse that stymied Bill Clinton - another young charismatic Democrat with great potential. In foreign affairs, Obama's addiction to his own rhetoric and charisma is more apparent, and more dangerous. Foreign policy has often been a refuge for modern presidents, an arena for bold actions, stirring speeches and fawning headlines with less congressional or press interference. But many major presidential disasters of the past half-century were rooted in foreign troubles. Most people forget that the phrase "the best and the brightest" - which has been used repeatedly to boost Obama and his Ivy League advisers - was more epitaph than tribute in David Halberstam's classic work on Vietnam. John Kennedy's people, despite his charisma and eloquence, despite their smarts and pedigrees, steered America into the bogs of Indochina. So far, while his actions in boosting troops in Afghanistan and keeping troops in Iraq have been measured, Obama's instincts abroad have proved troubling. Reacting feebly to in-your-face North Korean missile tests and initially dismissing heroic Iranian protests while belligerently targeting Israeli settlements further evokes unhappy memories of Jimmy Carter, who incompetently alienated friends and appeased enemies. OBAMA'S CAIRO speech revealed his characteristic tendency to hover above the fray, create moral equivalencies between opponents and promise to reconcile the unreasonable combatants. World affairs are rarely that simple. Naivete and moral obtuseness usually fail, even if George W. Bush proved too heavy-handed, simplistic and incompetent. Still, the presidential learning curve, especially in foreign affairs, can be steep. The presidency, despite being the world's most scrutinized job, is also ever-changing, providing more plot twists than an Alfred Hitchcock movie. Nikita Khrushchev bullied John Kennedy when they first met in Vienna in 1961, only to be outmaneuvered by a more experienced JFK during the October 1962 Cuban missile crisis. And Israelis forget that George W. Bush, whose warm friendship for Israel seems to have put off Obama, did not enter the White House as an obvious friend. Well into Bush's first year in office, Bush - or his secretary of state Colin Powell - criticized nearly every Israeli action against Palestinian terrorism, which mounted with increasing intensity that awful year. Only the horrors of September 11, 2001 - followed in January 2002 by Yasser Arafat's direct lie to Bush claiming not to know anything about the Karine-A illegal arms shipment from Iran - changed Bush's approach. A now-famous YouTube video shows Obama killing a fly easily during a television interview. Obama gloats at his success, which was cool and impressive. As he governs, Obama has demonstrated great potential but even greater confidence. Whether his cool personality roots him, or his arrogance defeats him, remains to be seen. Ultimately, results not charisma will count. The writer is professor of history at McGill University, on leave in Jerusalem. He is the author of Why I Am a Zionist: Israel, Jewish Identity and the Challenges of Today. His latest book The Reagan Revolution: A Very Short Introduction has just been published by Oxford University Press.