Bernd Debusmann(Bernd Debusmann is a Reuters columnist. The opinions expressed are his own)

By making the war in Afghanistan his own, declaring it a war of necessity and sending more troops, President Barack Obama has entered a race against time. The outcome is far from certain.

To win it, the new strategy being put into place has to show convincing results before public disenchantment with the war saps Obama’s credibility and throws question marks over his judgment. Already, according to public opinion polls in August, a majority of Americans say the war is not worth fighting. Almost two thirds think the United States will eventually withdraw without winning.

There are similar feelings in Britain, which fields the second-largest contingent of combat troops in Afghanistan after the United States. A poll published in London this week showed that 69 percent of those questioned thought British troops should not be fighting in Afghanistan.

In the United States, almost inevitably in a country that never forgot the trauma of the only war it ever lost, 36 years ago, pundits are conjuring up the ghost of Vietnam. A lengthy analysis in the New York Times wondered whether Obama was fated to be another Lyndon B. Johnson, the president who kept escalating the Vietnam war.

The war in Afghanistan is drawing into its ninth year and chances are it will still be going badly when Obama is gearing up for his campaign for re-election in 2012. According to a study by the RAND institute, a think tank working for the military, counter-insurgency campaigns won by the government have averaged 14 years.