Senator Miller of Georgia gave the keynote address at a party convention in Madison Square Garden in 1992. He was backing the governor of Arkansas, William Jefferson Clinton, saying that President George H.W. Bush “doesn’t get” the concerns of working families.

Tonight the 74-year-old populist Democrat will take to the platform in the Garden again and explain to the nation why he is supporting President George W. Bush.

Since arriving in the Senate in 2000, the former Georgia governor, who co-chaired the Democrats’ 1996 platform committee, has grown increasingly alienated from his party. He recently authored a book – “A National Party No More: The Conscience of a Conservative Democrat” – attacking Democrats for serving special interests.

Yet Mr. Miller refuses to switch parties, often comparing the party to “an old house” he helped build and in which he would like to live out his days, rather than hand it over to newcomers.

Republicans are feting him at this week’s convention. “He’s a celebrity in our delegation,” said a spokesman for the Georgia Republicans, Marty Klein. Some 400 people turned out for a party in his honor on Monday evening at Anthem Gallery in SoHo.

“The convention gives Mr. Miller a chance to look in America in the eye and articulate why this president is the right man at the right time and why he has crossed party lines to support the president for reelection,” said Bush-Cheney campaign spokesman, Kevin Madden.

Democrats, though, remain mystified and angry. They are spending $35,000 to rebroadcast Mr. Miller’s 1992 speech on several Georgia television stations this week.

“It was a great speech. A lot of what he said holds even more true today,” said the chairman of the Democratic Party of Georgia, Bobby Kahn. “I’m just waiting in anticipation for him to explain his conversion from a champion of working families to a defender of special interests in Washington,” said Mr. Kahn.

“He co-chaired Al Gore’s leadership PAC in 2000.And now, all of a sudden, in 2004 he’s decided the party’s too liberal? What’s changed? On what issue has the party moved to the left from where it was when Zell was writing our platform?” said Democratic strategist Paul Begala, a speechwriter on Mr. Miller’s 1992 DNC address, in a statement on the party’s Web site.

Polls show that the prospect of tonight’s speech has not hurt Mr. Miller politically in a state that now leans Republican in the presidential race. But neither is he seeking political advantage. His term ends in January 2005 and he has said he will not run for re-election. He is expected to return to an academic post – he had been a history professor – or to sit on the corporate boards he left before coming to Washington.

Mr. Miller is “by far the most popular politician in Georgia,” said the CEO of the national polling firm Insider Advantage, Matt Towery.

After announcing he would be speaking at the Republican convention, he retained his approval rating of 64% – the highest in the state, according to a poll taken on June 1. Even 54% of Democrats in the state approve of him, showed the poll, which had a margin or error of six percentage points.

Mr. Miller has said that September 11th was the turning point that brought him to side with President Bush. But the beginnings of his conversion predate the terrorist attacks, observers say. Mr. Miller embraced the president’s education initiative and was the first Democrat to back the tax-cut bill.

“After the election he went out to Crawford to meet with President Bush, and was right out of the box supporting Ashcroft,” said Mr. Kahn, who was the chief of staff to then governor Roy Barnes, who appointed Mr. Miller in July 2000 to fill the seat left vacant by the sudden death of Paul Coverdell. “It seemed like a good idea at the time,” he said.

Mr. Towery, a former Republican congressman from Georgia, speculated that Mr. Miller’s relationship with the party became strained when he arrived in Washington and began clashing with Democratic leaders in the senate.

“Part of that was result of the fact that he was a governor – and governors are not used to taking marching orders, particularly when the marching orders are for legislation that might not be popular at home,” he said.