Ric Francis / AP

By Karen Breslau 

Even the organizers at a Sunday afternoon rally for Barack Obama at UCLA had no idea they were about to pick up an endorsement from California's first lady Maria Shriver.  Fresh from a horseback ride with her daughter Katherine, 18, Shriver showed up at the last minute to join her cousin Caroline Kennedy, best friend Oprah Winfrey and Michelle Obama onstage. "There is no place I wanted to be but here today," said Shriver. "This election is about a moment. This is a moment not just for the United States of America, not just for the Democratic Party, but this is a moment for California. The more I thought about it, I thought, if Barack Obama was a state, he'd be California. Think about it: diverse, open, smart, independent, bucks tradition, innovative, inspiring, dreamer, leader."

Shriver's spontaneous endorsement stunned Clinton supporters in California, who say they'd been getting signals that -unlike other members of the Kennedy clan, most notably her Uncle Ted and her cousin and close friend Caroline-Shriver intended to remain neutral in the Democratic primary. Shriver's endorsement--the first she's given to a non-family member--also scrambles the impossibly convoluted political terrain in the "post-partisan" administration of her husband, Calif. Gov. Arnold Schwarzenegger, who last week endorsed Sen. John McCain. Among those blindsided by Shriver's Obama endorsement was Schwarzenegger's chief of staff, Susan Kennedy (no relation), a Democrat, who is a high-profile Hillary supporter - and whom Shriver brought in to help right her husband's listing administration when he got into serious political trouble a couple of years ago. Following?  "There is a time-honored truth that women are our own worst critics," Kennedy wrote in a email message to NEWSWEEK.  "Women are held to a higher, sometimes impossible standard in politics, in business, in media, in life -- especially by other women."

Hillary backers also want to know how Shriver plans to square her public backing of Obama with the signature issue of her tenure as California's first lady: promoting women's leadership? Each fall, Shriver hosts a giant, celebrity-studded event dedicated to celebrating women as "agents of change."  If Hillary turns out to be the Democratic nominee, after all, Shriver could have some explaining to do. 

Those close to Shriver insist her decision was deeply personal--she'd decided some time ago to vote for Obama, and had even told Hillary, to whom she's never been particularly close, in a phone call last week. They dismiss speculation that the notoriously headstrong Shriver would have caved to pressure from her Kennedy relatives to back Obama any more than Arnold could have convinced her to vote for McCain.  An endorsement from any celebrity is unlikely to have much impact only hours before an election. But it's sure to deepen the drama surrounding one of the country's most prominent bipartisan couples. Carville and Matalin, eat your hearts out.