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Has Zell Miller (search) lost his mind?

Some of his party members think so. Republicans think not. The retiring U.S. senator from Georgia has never shied from the outlandish, but this time is a doozy.

He is the keynote speaker at the Republican National Convention, endorsing President Bush for re-election while declaring, "I'll be a Democrat 'til the day I die."

"If they want to call me a leper or a traitor, that's OK with me," barked Miller, a 72-year-old former Marine, on Monday. "I've been called a lot worse. This is nothing."

It's much more than that to Miller's fellow Democrats, who have called him "an elephant in a donkey's clothing." He was tagged long ago with the nickname "Zigzag Zell" for his political shifts. Those are the nicer descriptions.

A group of Democratic campaign workers created a Web site, www.Zellout.com, demanding that Miller switch parties and declare himself a Republican.

On Wednesday night, Miller will deliver a prime-time address to the full convention, just after Vice President Dick Cheney. In 1992, as governor of Georgia, Miller gave the keynote speech introducing Bill Clinton, then governor of Arkansas, as the Democratic presidential nominee.

"For 12 dark years, the Republicans have dealt in cynicism and skepticism," Miller said then. "They've mastered the art of division and diversion, and they have robbed us of our hope." Of the then-incumbent president, George H.W. Bush, Miller said, "our commander in chief talks like Dirty Harry, but acts like Barney Fife."

Today, of that president's son, Miller says: "No one else can lead this country."

Miller was Georgia's lieutenant governor from 1975 to 1991. He was appointed to the U.S. Senate in 2000 following the death of a Republican incumbent, Paul Coverdell, and was elected later that year.

For years, rumors swirled that Miller would defect to the GOP, the state's new party power.

Miller remained a Democrat. But he doesn't always act like one.

In the Senate, he often caucuses with the Republicans instead of his own party, and just as often votes with them.

And here in the Big Apple, he is a much sought-after man.

Since arriving on Sunday, Miller has been so solidly booked for interviews during the four-day convention that his GOP handlers now decline all media requests. He participated in a forum with ultra-conservatives such as Ann Coulter, discussing the impact of conservative books on American politics.

Georgia Gov. Sonny Perdue and the state's GOP delegation were welcoming Miller on Monday with two-hour reception at a Soho gallery. On Thursday, conservative economic group The Club for Growth plans a "Tribute to Zell Miller" and the posh University Club.

"I have never voted for a Republican in my life," Miller said. In 1952, he voted for Adlai Stevenson. In 2000, he voted for Al Gore.

So why vote GOP now?

"I think the times demand it," he declared.

Because of the threat of terrorism?

"Of course because of the threat of terrorism," he retorted. "What else? Nine-11 changed everything."