In the aftermath of Obama's acceptance speech, many have analyzed and interpreted his statement that he is, obviously, the president.
To some it meant asserting his status as alpha dog. To some it was an apology for hope unfulfilled and dreams deferred. For some it was a wistful yearning for simpler times.
A crisis like the current one, however, illustrates clearly what it means to be the president rather than a candidate.
A candidate is applying for the job without actually having to do it. His (or her) main concern is the campaign. He can afford to look at foreign and domestic affairs from the "How does it affect my campaign?" perspective. He can afford to get the first tweet or presser out when sh*t happens. He can choose (or not) to exploit the situation for political advantage.
All the while, the president is already doing the job for which the candidate is applying. He must (if he does what he's supposed to) consider the well-being of the country and its citizens above his own poll numbers and approval ratings. He must set different priorities than a mere candidate would. When tragedy strikes, he must minimize the damage, not to his own reputation but to the nation he was elected to lead.
For a president, sometimes a phone call to a foreign leader, a trip to a disaster zone, or a meeting in the situation room has priority over a press conference or comment on his opponent.
What a candidate says and does could get him elected or imprint the loser L forever on his forehead. What a president says and does could either resolve a crisis or trigger a war.
When the 3 a.m. call comes, a candidate can afford to analyze, interpret, and evaluate. The president has to answer the phone.