Over the past several days, pundits from across the political spectrum have declared Wednesday night's third and final presidential debate the last opportunity for John McCain to turn around his political fortunes. But as the final encounter between the two candidates demonstrated, such advice was divorced from the reality of this increasingly one-sided campaign. Behind in the polls and lacking a clear economic message, there was little that Mr. McCain could have done to change the fundamental dynamics of this race: a fact borne out in last night's debate.

The advice given by some pundits to Mr. McCain hardly reflects the reality of presidential campaigns, which are like ocean liners -- nearly impossible to turn around on a moment's notice. Once they settle in a specific direction, that is generally the direction they are going to go, and the closer they come to their destination (in this case, Election Day), the harder it is to change course. Candidates can't just pull winning messages out of the air in the final three weeks of a campaign, and Mr. McCain who rather decisively lost the first two debates with Barack Obama was not about to turn into the second coming of Abraham Lincoln or Stephen Douglas.

For Mr. McCain, decisions made days, weeks even months ago placed him in the unenviable political position that he found himself last night; just as decisions that Mr. Obama made earlier this year placed him at the cusp of a historic political victory.

For example, Mr. Obama holds a sizable advantage on the economy (one that has been bolstered by the nation's financial crisis). But this advantage didn't occur overnight. It came because Mr. Obama was speaking coherently about the issue months ago, relating the concerns of the middle class to his own domestic priorities. When trouble hit in the beginning of September, Mr. Obama was more than prepared to seize the political moment.

Conversely, Mr. McCain's almost stubborn refusal to lay out a cogent economic message, particularly at the G.O.P. convention, where he focused more on his personal character, rather than the travails of the American middle class, fatally hamstrung him. Once again on Wednesday night, he demonstrated an inability to empathize with the plight of Americans suffering from the economic downturn. His constant invocations of "Joe the Plumber," while possibly effective at first, became grating as the debate wore on.

Even more striking than the economy was health care. Back in the spring, Mr. McCain laid out a plan that was basically a regurgitation of President Bush's unpopular policies: more or less ceding the issue to Democrats. So it should be little surprise that in the final presidential debate, he sputtered through a question on health care, talking about electronic health records and school nutrition programs while Mr. Obama coolly and empathetically described his plan -- and tore apart his opponents'.

As he has done throughout the election season, Mr. Obama, on Wednesday night sought to tie his opponent to the deeply unpopular policies of President George Bush. Since the beginning of the general election, Mr. Obama has made this the centerpiece of his attacks against Mr. McCain and really, who can blame him. Few presidents, if any, can rival the sheer loathing that Mr. Bush seems to evoke among the American people.

This fundamental reality was always going to be a problem for any Republican who sought the White House in 2008, which made it that much more important for the G.O.P. standard bearer to separate himself from the toxic resident of 1600 Pennsylvania Avenue. Mr. McCain hasn't done it. Last night, he said to Mr. Obama, "I am not President Bush, if you wanted to run against President Bush you should have run four years ago. I will take this country in a new direction." It was his best line of the night, but it came too little, too late to have an impact on the race.

In fact, Mr. McCain offered little evidence as to how he would take the country in a new direction hewing to a surprisingly conservative line as he hit right-wing touch points like school vouchers, cutting business taxes and broadsides against government spending. That Mr. McCain still feels a need to play to his conservative base less than three weeks before Election Day is striking.

Looking back, Mr. McCain's best hope was always to scare the American people about the possibility of an Obama presidency. The extent to which Mr. McCain has misfired on this objective is stunning. Since the summer, the McCain campaign has veered from attack to attack; first comparing Mr. Obama to a celebrity, then calling him too liberal, then saying he lacked experience, then accusing him of "palling around with domestic terrorists." Again last night, Mr. McCain failed to develop any coherent or consistent negative argument, even undercutting his own campaign's attacks about Mr. Obama's relationship with William Ayers by saying he doesn't really care about an "old washed-up terrorist" and then absurdly declaring that ACORN, a small non-profit organization, is "maybe destroying the fabric of democracy."

Despite Mr. McCain's constant drumbeat of demonizing personal attacks against Mr. Obama, it's telling that the Democratic candidate is now seen more favorably than Mr. McCain and more likely to share the same values of the electorate. When one considers that practically all of Mr. McCain's ads are negative this seems almost unimaginable. If politicians could sue their consultants for political malpractice, Mr. McCain would certainly have cause to haul his campaign manager, Steve Schmidt, into court. Mr. Schmidt has taken one of the most respected politicians in America and turned him into something and somebody quite different.

In the end, tonight's debate contained few surprises and no real diversions from the long-ago established course of this campaign. Mr. Obama led going into last night, he led when the evening was over and there wasn't a lot that John McCain could do about it. With 19 days until voters make their choice, the die has been cast: anything other than an Obama victory on Election Day seems difficult to imagine.