(Joe Burbank/Orlando Sentinel/MCT/Newscom; BRENDAN SMIALOWSKI/AFP/GettyImages)

ANALYSIS

CHARLOTTE, N.C. - President Obama has met his own worst enemy, and his name is Barack Obama.

As the Democratic National Convention gets underway this week in North Carolina - a state that epitomized the Obama wave of 2008 but has slipped steadily from the Democrats' grasp since then - memories of the hope and expectations the president embodied four years ago loom over the gathering.

It's a sentiment more threatening to the president's reelection chances than the caricature of an ineffective president perpetuated by some on the right.

That's one reason that version of the president was barely introduced when the GOP's own convention, a gathering that seldom lacks red meat, was held last week.

"You know there's something wrong with the kind of job he's done as president when the best feeling you had was the day you voted for him," Mitt Romney said last week in accepting the Republican presidential nomination.

The optimism that's morphed into uncertainty colors the lackluster economic statistics that are a drag on the president's reelection prospects.

It's why Paul Ryan's apocryphal story of the 20-something living back home with his parents, staring at a faded Obama '08 poster, stands as the most enduring image of last week, this side of Clint Eastwood's empty chair.

This week is particularly challenging for the president because it invites comparisons to his past convention speeches. Gatherings like this one contributed to the lofty expectations that powered Obama to the presidency, despite the brevity of his national political career.

The president burst onto the national landscape in Boston in 2004, with a clarion call to move beyond red- and blue-state identities for a common good.

His commanding performance four years later - amid the columns and literally on the mountaintop in Denver's clear air - was the apex of his promise and his appeal.

"What has also been lost is our sense of common purpose," candidate Obama said four years ago, "and that's what we have to restore."

But governing has proven more difficult. Promises about ushering in a new era of politics evaporated with Capitol Hill realities around a stimulus bill, a bitter health care fight, and then the rise of the tea party movement that turned back the president's army in Congress.

It is therefore disillusionment more than anger that represents the president's most formidable adversary. That will take battling throughout the week, in the push to fill a stadium, and fulfill a promise that isn't so old, but has seldom felt more distant.

The president's challenge is also his opportunity: to fill that chair with presidential leadership, and to deliver an argument for keeping himself firmly planted in that seat for another four years.