In a primary election as unusual as this one, it's dangerous to get too confident when drawing conclusions, but here are a few educated guesses about how Perdue won the primary today.
She was the frontrunner. As a two-term lieutenant governor and longtime legislator with a bevy of endorsements from big groups, Perdue was the favorite from the start and Moore never managed to knock her down.
She had good issues. Perdue had a good portfolio on both soft issues (health care, education) and hard issues (the military). Moore's issues were more national (climate change, Wall Street reform) and wonky (the line-item veto, transportation reform).
She benefited from high turnout. Perdue had strong support among women and black voters, two groups that were energized by the unusually competitive presidential primary between Hillary Clinton and Barack Obama.
She went positive. Perdue and Moore both ran nasty campaigns through the fall, but Perdue went positive just as most voters started paying attention. That endeared her to Obama's "change" voters, won points for gutsiness and made Moore's attacks look bad.
She had fewer enemies. Moore manages the state pension fund? State employees sue him. Moore crusades on Wall Street? Forbes magazine attacks his campaign funding. Moore makes his case on education? The N.C. Association of Educators attacks him.
Moore never succeeded in opening any daylight between his campaign and Perdue's. When he endorsed Obama, she endorsed Obama. When he called for raising the minimum wage, opposed coal plants at Cliffside, etc. etc., so did she.
With the wind at her back from turnout, endorsements and expectations, Perdue managed to stay in the lead throughout the primary despite early missteps.