During the past two weeks, the dynamic of the 2012 presidential election has shifted, and President Obama has moved out to a modest but significant lead against Mitt Romney. No developments in the economy or the world can explain this shift. That leaves the campaigns themselves. And during the past two weeks, Romney’s campaign has revealed itself to be stunningly incompetent.

Let’s start with a key structural feature of the 2012 campaign: Romney’s challenge has always been to keep his distance from the party he is leading—the Republican Party, after all, is farther ideologically from the median voter than is the Democratic Party. And as recently as a few months ago, Romney was in good position to do just that: While the public has seen Barack Obama and his party as more or less indistinguishable, they have viewed Romney as a moderate conservative within a highly conservative party.

But, astoundingly, his convention managed to achieve precisely the opposite of what it needed to. The Republican convention was a three-day display of what the Republican Party has become, and by the end of it, Americans viewed Romney, not just as an individual, but as the standard-bearer of his party. Only 36 percent of those who listened to or watched the Republican convention said that it made them more likely to vote for Romney, versus 46 percent less likely. As far back as 1984, there is no precedent for a convention that repels more voters than it attracts. Indeed, during the past three decades, national conventions have generated—on average—a positive response (more likely minus less likely) of 18 percentage points. So while the impact of the Democratic convention (plus 10) was below average, the Republicans managed to stage the least effective convention in modern political history.

And that disastrous convention was soon reflected in the polls. On September 5, the average of national polls showed the candidates in a dead heat at 46.8 percent of the popular vote; by the 13th, Obama’s support had risen to an average of 48.6 percent, while Romney’s fell to 45.3 percent, and Obama had moved out to a lead of 3.3 points. (Recent reports suggest that the Democrats backed up their convention with a pedal-to-the-metal advertising barrage in battleground states.)

Meanwhile, since the end of the convention, the president has run an effective and efficient campaign. He has a theory of the case and a strategy to match it. By contrast, Romney has been campaigning at a pace that can charitably be described as languid, lurching from one tactical statement to the next without a consistent theme or strategy.