With polls showing Bush in a neck-and-neck battle for the White House against Democratic rival John Kerry, the convention's battle cry is in defence of the war in Iraq and the global "war on terror".
Senator John McCain hailed Bush's leadership since the attacks and dismissed any suggestion that his fight against terrorism was unjustified.
"Only the most deluded of us could doubt the necessity of this war," he said in a speech repeatedly interrupted by applause. "President Bush deserves not only our support, but our admiration."
But even as the accolades came thick and fast inside the convention centre at New York's famed Madison Square Garden, thousands of people demanding social reforms protested on the streets outside on Monday.
"It's a shame that in the richest country in the world twelve million children are hungry every night," cried an activist from a small platform in front of UN headquarters, galvanising a crowd of protesters under the watchful eye of police clad in riot gear.
"It's a shame that in the richest country in the world twelve million children are hungry every night"
Activist at anti-Bush protest march
Several thousand pacifists, anarchists, union members, defenders of the poor and others gathered on Monday at midday - one of two large marches of the day in Manhattan -demanding social justice.
For them, opposing Bush was not just about marching against the war in Iraq. They were highlighting the lack of social progress in their own country under the Bush administration.
The ranks of the financially stricken in the world's most powerful economy climbed 1.3 million to 35.9 million people in 2003, pushing up the poverty rate to 12.5% from 12.1%, the Census Bureau said in figures released on Thursday.
It is the third year in a row that it has increased and the highest poverty rate since 1998 when 12.7% of Americans lived in poverty.
But there was protest of a different kind at the Republican rally. The audience thunderously jeered filmmaker Michael Moore and his anti-Bush documentary Fahrenheit 9/11 when McCain mentioned it in his speech.
As Moore looked on from the press gallery, McCain took the film to task while defending the decision to invade Iraq as the choice between "war and a graver threat".
Michael Moore has created quite
a stir by turning up as a reporter
"Don't let anyone tell you otherwise," he said.
The film savages Bush's Iraq policy, accusing him of lying about the reasons for the war and going after the wrong enemy. Fahrenheit 9/11 has set a box office record for documentaries, grossing $115 million so far.
Bush has made fighting terrorism the cornerstone of his re-election attempt, and speaker after speaker referred to the September 11 attacks which demolished the World Trade Centre towers that stood just 5km from the convention site.
Place in history
Rudolph Giuliani, mayor of New York City at the time, said Bush's reaction to the attacks had already "earned [him] a place in our history as a great American president".
Nearly 5000 delegates and thousands of other guests jammed the convention centre, decked out in red, white and blue for the Republican gala that will climax when the president arrives on Thursday.
John Kerry has been called 'weak
on the war and wrong on taxes'
Bush and Vice-President Dick Cheney will face Kerry and running-mate John Edwards when voters cast their ballots on 2 November, an election touted by both sides as the most important in a generation.
But while McCain held off from personally attacking Kerry, other speakers ridiculed the Democratic senator from Massachusetts.
"This is no time to pick a leader who is weak on the war and wrong on taxes," said Dennis Hastert, Republican speaker of the House of Representatives.
The constant reference to the attacks on the World Trade Center, however, may be creating a backlash that accuses the Republicans of exploiting both New York City and the ordeal it endured four years ago.
A New York Times poll of 339 relatives of victims found that more than half of them would have preferred the Republican Convention to be held elsewhere.
But like the rest of the population, this small group seemed clearly divided in its views.
A quarter thought Republicans chose New York "to capitalise on September 11" and another quarter believed that, on the contrary, the point was "to show it's safe".
"I don't think either party, Republican or Democratic, should be using 9/11 as any kind of political backdrop, because both have failed. Why 9/11 occurred, it's because there's been so many failures," said Bill Doyle, father of a man killed in the World Trade Centre.
In Doyle's view, Bush "knows that if he gets into too much 9/11, there could be a backlash". When Bush ran an early campaign advertisement with a fleeting image of firemen around a flag-draped coffin, it touched off days of polemics.
Terry Rockefeller, sister of a victim and member of the group September Eleventh Families for Peaceful Tomorrows, marched at the front of an anti-Bush demonstration on Sunday "to let the nation and the world know that many of us never wanted this illegal [Iraq] war in the name of our loved ones".
The group said it would march in Manhattan during the convention with a gravestone for "unknown civilian killed in war".