By freeing his campaign from the public system, Mr. Obama can continue to raise donations from his vast base of supporters, who have made his campaign thus far the best-financed in history. Mr. Obama is rightly counting on them to raise far more than the $84 million in public funds he could expect to receive from public financing.

Some observers make the case that money is less important at the presidential level because the press plays such a significant role in communicating the campaign narrative. But money still counts for much and a financial advantage is vital to a candidate who expects to come under heavy attack. In 2004, conservative groups ran negative ads against Senator John Kerry and inflicted substantial, arguably fatal, damage to his presidential campaign, giving us the verb “to swift boat” as a linguistic bonus. While no similar ad campaign is yet under way against Mr. Obama, the chances that he will skate to November without sustaining a barrage seem slim.