CHARLOTTE, N.C. - Why did the Obama campaign fumble the "are Americans better off than four years ago" question?

Why has President Obama been unable to put the "you didn't build that" charge to rest?

And why has the campaign struggled to come up with a coherent response to the Republican convention? (Calling it a pack of lies doesn't count.)

It's hard to avoid the conclusion that, as Democrats begin their convention here in Charlotte, the Obama campaign is not hitting on all cylinders. The question is why a campaign that was so successful in 2008 is sputtering today.

Here's a theory: Barack Obama has never in his life run against a sharp, determined and aggressive Republican opponent. Facing Mitt Romney, who is all three, is a new experience for the president.

Look at Obama's political career. He won his first election to the Illinois Senate in 1996 mainly by challenging signatures on his Democratic primary opponent's candidacy petitions and getting her kicked off the ballot.

Re-election was no problem in Obama's heavily Democratic district. The only race he would ever lose came in 2000, when he mounted a primary challenge against Democratic Rep. Bobby Rush for a seat in Congress. Republicans were not a factor.

When Obama ran for U.S. Senate in 2004, both his Democratic primary opponent and Republican general election opponent imploded when their (ugly) divorce records were made public. Obama ran for a while with no opponent at all until GOP gadfly Alan Keyes moved to Illinois to offer weak opposition. Obama won in a landslide.

In 2008, Obama faced the race of his life against Hillary Clinton in the Democratic presidential primaries. He ran a good campaign but was also aided by some inexplicable Clinton mistakes in which she failed to exploit the system by which Democratic delegates were awarded.

When the general election came around, Obama faced a Republican opponent, John McCain, who had lost a step from his GOP primary run eight years earlier, whose campaign was riven by internal turmoil, and who simply was not determined to do what it took to win.

McCain's challenge was so weak that today Obama sometimes waxes nostalgic for the good old days of perfunctory GOP opposition. "The last time we ran, we had a Republican candidate who -- I had some profound disagreements with him, but he acknowledged the need for immigration reform, and acknowledged the need for campaign finance reform, acknowledged the need for policies that would do something about climate change," Obama said at a June fundraiser in Chicago."Now, what we've got is not just a nominee but a Congress and a Republican Party that have a fundamentally different vision about where we need to go as a country."

And not just with a different vision -- a different idea of how a campaign should be run. From the very beginning, the Romney campaign has signaled its intention to run a hard-hitting, sharp-elbowed race. Obama has never been on the receiving end of that from a Republican before.

"We're running an aggressive race that is focused on highlighting the president's failed policies and holding him accountable for his own words and his own record," says a Romney aide. "At times, the president's campaign shows that they can dish it out, but they can't take it."

And it's not just attacks on Obama's job performance. It's ridicule, too. In 2008, it would have been simply impossible to imagine Obama mocked during a National Empty Chair Day, as happened Monday, building on the improvised standup routine delivered by Clint Eastwood at the Republican convention. But that's what the president is facing now.

Running in a primary, even a tough primary, is different from a general election. In a primary, a candidate speaks to party regulars who pretty much agree on principles but are looking for the best messenger for the party. In a general election, there's a clash of fundamental ideas, argued before the public at large.

In 2008, McCain was so lackluster, and conditions so bad for Republicans, that Obama wasn't really challenged. Now, he is.

In the next two months, Obama can count on being attacked, questioned, and -- perhaps worst of all -- made the butt of jokes. Of course he's taken his share of criticism in the White House, but he's never experienced that going down the stretch in a general election. He'll have to learn to deal with it -- or lose.

Byron York, The Examiner's chief political correspondent, can be contacted at His column appears on Tuesday and Friday, and his stories and blogposts appear on