Campaigning reached a fever pitch this weekend, as the US leader criss-crossed the United States in the final days before the balloting, in hopes of shoring up the Republicans' conservative base.
Analysts predict steep Election Day Republican losses for Bush's party, which could greatly change the tenor of the final two years of his administration, after a Republican majority for the first six.
Polls show the party's declining fortunes to be linked to the unpopularity of the war in Iraq, where raging sectarian violence risks worsening in reaction to a coming verdict in the trial of deposed Iraqi dictator Saddam Hussein.
A recent CBS poll showed Iraq to be by far the most important concern of voters, with 27 percent citing it as their top-priority issue, followed by the economy and jobs (13 percent), illegal immigration (eight percent) and terrorism (seven percent).
But while many of Bush's fellow Republicans are avoiding speaking about the war, the president is defiantly embracing his decision to invade Iraq.
"I made the right decision to get rid of Saddam Hussein, and the world is better off for it," Bush said to thunderous applause at a campaign stop in Iowa on Friday.
The US leader also pressed one of the central tenets of his presidency: that the prosecution of the war in Iraq will help prevent acts of extremism in the United States, such as the September 11, 2001 terror attacks.
"One of the lessons of September the 11th is this -- and it's a lesson no president can ever forget -- that when we see a threat, we must take that threat seriously before it comes home to hurt us," Bush said.
The issue still resonates with voters who put a premium on winning the war against terrorism. But some political observers believe voter anger over the war on Iraq could lead to a Democratic show of force on election night.
Polls show Democrats with leads in numerous key races, and pundits were increasingly confident in predicting a power shift in the US House of Representative, and possibly the US Senate as well.
With Democrats needing a net 15 seats out of 435 in play to control the House, and six seats out of 33 to dominate the 100-seat Senate, respected Washington pundit Charlie Cook was forecasting "a very strong Democratic wave" on Election Day.
A new Washington Post-ABC News poll published on Sunday found that in the battle for the House, Democrats appear almost certain to pick up more than the 15 seats needed to regain the majority. Republicans virtually concede 10 seats, while about 30 additional toss-up races were likely to yield to the Democrats 15 more seats, according to the survey.
In the Senate, the Democrats are virtually assured a three-seat gain, but they would have to find the other three seats from four states considered to have tossup races -- Virginia, Tennessee, Missouri and Montana, the poll indicated. "It's the worst political environment for Republican candidates since Watergate," The New York Times quoted Glen Bolger, a Republican pollster, as saying.
As control of the Congress hung in the balance, Bush appealed to bedrock conservative "values voters" who make up his base.
Republicans also were counting on their vaunted voter turnout machine to stem election losses and allow them to maintain their majorities in the House and the Senate.
But it remains to be seen whether the president will help or hinder Republican goals of holding onto power. And the need by Bush in waning days of the race to defend Republican-friendly turf in "red" states such as Nebraska and Kansas was seen as a sign of desperation in some quarters.
"Perhaps the most remarkable thing about this election is that Republicans are having to fight and spend money in states and districts where few Democrats have dared tread in recent years," Cook wrote in his Cook Political Report.
"This still looks to be a very ugly midterm election for the GOP," he said.
Voters in 36 states also are casting votes for governor Tuesday. Democrats hold significant leads in five of nine open seats: Ohio, Arkansas, Colorado, New York and Massachusetts, and are favoured to displace Republicans in Maryland, Arkansas, and Minnesota.
That sets up the possibility that Democrats could gain a solid majority of governorships for the first time since 1994.

Copyright AFP (Agence France-Presse), 2006