America is near the end of the longest democratic succession struggle in world history: 23 months ago the first candidate threw his hat in the ring. By comparison, Bill Clinton was considered an early entry when he announced in October 1991, just 13 months before the 1992 election.

Not only did this race get going earlier, it got going harder as well. Democrats had their first primary debate 22 months ago and their second a month later.

This will be America’s most costly presidential race. Barack Obama will spend north of $700m and John McCain more than $450m. Add the other candidates and third-party groups and the total expenditure will break $2.4 billion.

This may seem a lot but Americans annually spend $8 billion on haircare products, $64 billion on soft drinks and $577 billion on convenience store purchases, so $2.4 billion isn’t too much to pick the leader of the free world.

How America's presidents rated

The Times has ranked all 42 US presidents - was Bush Jr. bottom? Did JFK beat Abraham Lincoln?

Related Links

• Obama has the White House within his grasp

• Whites and Wal-Mart women give McCain hope

• How they tried to tarnish Obama

Neither party’s original front-runner survived. As late as January the polls still predicted a Clinton-Giuliani race. It was the luck of McCain and Obama that the early contests favoured them, with New Hampshire providing McCain with a decisive victory and Iowa giving Obama a spectacular launch.

Both nominees still won with a minority of the primary vote. Obama beat Hillary Clinton on votes and delegates through March, but received fewer votes and elected delegates between March and June. It was his early lead that allowed him to withstand her late charge. Ironically, Obama secured the nomination because of his support among “superdelegates”, the Democrats’ very own House of Lords.

Both tickets are improbable. McCain is barely tolerated by many in his party, having spent years irritating Republican congressional colleagues, exasperating party leaders and frustrating grassroots activists.

This experienced warhorse chose as his running mate Sarah Palin, the Alaska governor who can shoot a moose, field dress it, fillet it and fix it.

Democrats selected Obama, the first African-American to head a major party ticket. This freshman senator doesn’t have a single significant legislative accomplishment or record of bipartisan action since coming to Washington. This hasn’t stopped him from centring his campaign on a call for bi-partisanship and, heeding Martin Luther King’s invocation of “the fierce urgency of now”, a demand that leaders must confront America’s big challenges.

This candidate of change chose as his vice-president the sixth most senior senator, Joseph Biden, first elected when Obama was 11 years old. Biden has that mix of longevity and long-windedness that passes for wisdom in Washington.

The election has been dominated by two conflicting impulses. One is the desire for change that comes when one party has held the White House for eight years, strengthened by economic chaos and a lengthy war, which boosts Obama. On the other hand, there is persistent concern that he lacks the experience to be president. A March ABC/Washington Post poll found 45% of Americans felt Obama was unqualified. By October 29, 44% still felt that way. This is the worst unqualified rating since Michael Dukakis in 1988.

Both candidates know America remains a centre-right country. McCain has received his greatest traction from the success of the Iraq surge, which appeals to Americans’ desire for victory, and on taxes and spending, where he has contrasted his conservatism with Obama’s liberalism. Obama’s exchange with Joe the Plumber, an Ohio small businessman, helped McCain when Obama revealed that his tax increase was aimed at “spreading the wealth around”. Americans are instinctively against class warfare and redistribution; 73% of the top 1% whom Obama would tap for an estimated $131 billion in higher taxes each year are small businesses.

Because Obama recognises that America is a centre-right nation, he balances calls for withdrawal from Iraq with tough talk about stepping up US military efforts in Afghanistan, even threatening to invade Pakistan if that country fails to do enough to hunt down Al-Qaeda. He doesn’t emphasise his call for tax increases or income redistribution, but masks his policy as “a tax cut for 95% of Americans”. His adverts savage McCain’s health-care proposals as a tax increase and attack “government-run healthcare” as “extreme”. Obama has wisely used his financial advantage to press these points in “red states” to try to diminish the traditional Republican edge among evangelicals, military families, gun owners and small business owners.

What do the polls say about the race? There has been an explosion of them this year with 747 national head-to-head match-ups, 234 in October alone. By comparison, there were 235 national polls in all of 2004. But volume doesn’t produce clarity. On Thursday there were 10 national polls, with the margin from three points to 13 points. If the margin is three points, McCain has an uphill fight but can win. If it is 13 points, McCain’s task is essentially impossible. One thing has been consistent: his last national lead was on September 25 and he has trailed in all 251 polls since then.

If the margin between McCain and Obama is three points, there are more than enough undecided voters to swing the contest. Since 1948, undecideds have given an average of 38% to the challenger party, 34% to the White House party and 6% to third parties while 23% stayed at home. But this is not an average contest and no one really knows. Do undecideds want change or are they nagged by doubts that Obama is up to the job?

If McCain wins, he will almost surely face a Democratic Congress, which would mean divided government and compromise. If Obama wins, America will have one of the West’s most liberal governments – more liberal, in my view, than Britain, France, Germany, Italy and almost every other nation on the European continent, to say nothing of Canada. We will know in a few short hours.

Karl Rove is the former deputy chief of staff to President George W Bush

Times Recommends

• Tiger ‘was fleeing his angry wife’
• Cabal seizes diamond riches to buy power
• White House gatecrashers got to the president