Americans across the political spectrum believe the war in Afghanistan is futile and want to bring the troops home, according to a new a New York Times/CBS poll.

Support for the American mission in Afghanistan has eroded steadily as the conflict has dragged on for more than a decade, and the deteriorating situation over the last month appears to have sharpened that disillusionment. American troops provoked violent riots by burning Qurans and other holy texts, and a rogue American soldier later went on a killing spree that left 17 Afghan civilians dead.

A clear majority of people polled, 69 percent, said the United States should not be in Afghanistan. A similar proportion, 68 percent, said the war was faring somewhat badly or very badly. Both of those figures are substantial increases from a November New York Times/CBS poll gauging public opinion on the war.

Republicans, Democrats and independents all showed signs of war weariness, although the opposition was less pronounced among Republicans. Three in 10 Republicans said the U.S. should remain until Afghanistan is secure, compared with two in 10 independents and a mere one in 10 Democrats; a slightly smaller number of Republicans said the war was going poorly.

Although the Quran burning and the massacre have likely fueled public discontent, an ABC News/Washington Post poll conducted immediately just before the Times/CBS survey also found Americans turning against the war. In that poll, a majority of Americans said the war had not been worth fighting, and people who felt strongly the war had been a mistake outnumbered those who felt strongly it had been necessary by a three-to-one margin.

Despite the conflict's mounting unpopularity, the top American military commander for Afghanistan told lawmakers last week that the United States should maintain significant combat power in order to hold onto security gains. Marine Gen. John Allen did not outline a timetable for the full withdrawal of U.S. troops, saying he would assess that later in the year. The U.S. has agreed to have all troops out of the country by the end of 2014.