The tension in the two camps is almost visceral.
Rove's revolution could be over this November
It is hard to imagine a political race with greater significance than this one. As one of my colleagues in the American press said to me recently, "it's only going to decide the future of the free world."
It is the first election of the post-9/11 United States. It is a referendum on America's biggest military engagement since Vietnam and America's role in the world.
But for the two political parties, the result is critical to their survival.
Rallying the base
If the Republicans win a second term and retain their hold on Congress, the Democrats would probably be shut out of power for the rest of the decade.
On the other hand if the Democrats win, it will represent the failure of the Bush Doctrine, triggering a civil war within the Republican Party.
At the centre of this titanic battle sits Karl Rove, Bush's political adviser.
Rove has fashioned a unique political strategy around George Bush which relies more on motivating social conservatives than winning over moderates in the middle ground.
That's why George Bush has been unabashedly conservative in almost everything he has done, surprising even those within his own party.
He has clamped down on stem cell research, gay marriage and funding for abortion clinics abroad. He has portrayed himself as a tough, decisive, and, above all, principled leader.
When he lashes his opponent as a liberal on the "far left bank", Bush is not trying to win over the undecided voter.
He is firing up his base.
Liberal is one of those keywords that make social conservatives mad. Karl Rove believes there are more votes to be had in increasing the numbers of conservatives who go to the polls than in trying to bring in undecideds.
After the last election, he noted that four million evangelical conservatives did not bother to vote.
With a president like George Bush, he reasons it's easier to excite them than swing voters, for whom Bush's "with us or against us" view of the world might be a hard sell.
If Rove is right and he wins a second term for his boss, he will go down in the pantheon of great political operators.
If he fails, his boss will be remembered as a one-term Republican president who had no major impact on the course of Republican philosophy.
It's the difference between being a repetition of his father and being Ronald Reagan.
If Bush loses, "there will be civil war in the Party on November the 3rd," Pat Buchanan, the former Republican presidential candidate, told me this summer.
Conservatives will say that Bush's unusual mix of tax cuts and military interventionism failed because it departed from the straight and narrow of Conservatism which is small government, fiscal discipline and no foreign adventures.
And Karl Rove will be cast into the wilderness.
In the Democratic camp, success will spell the same thing: proof that the Bush Doctrine was a failed experiment.
The Democrats will have to decide who to appeal to
Failure for the Democrats, however, will raise serious questions about their viability as a party.
Why can't they pick a populist candidate? Has America shifted permanently to the right?
Does the Democratic Party need to reinvent itself? These are the sorts of questions the elders will ask.
The Democratic Party lacks the cohesive unity of the Republicans.
It is a motley and sometimes fractious alliance of Deaniac anti-war protesters, blue collar union men, aspirant yuppies, retired Jewish communities and soccer mums.
Some will say that the Party must return to its roots - whatever they are. Others will say it should stay with Clinton's centrist approach.
Whatever the outcome, it is going to be extremely painful for the losing side.
The stakes could not be higher. So don't expect it to be over quickly. Unless there is a clear Electoral College victory one way or the other on 2 November, both sides will dig in for a long legal fight.
They have too much to lose.
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