The context is very different now, without a military draft that fueled the Vietnam War's unpopularity and with a comparatively small force.
The 11-year Afghan war has not been highly popular among Americans for many years, but support has dropped off steeply. A year ago, 37 percent favored the war, and in the spring of 2010, support was at 46 percent.
The AP poll does not spell out why people have changed their minds. But the drop-off in support parallels rising casualties, increased attacks on Americans by the Afghan soldiers they are mentoring and inconclusive battlefield gains that have increased security in many areas of the country but have failed to break the Taliban-led insurgency.
About half of those who oppose the war said the continued presence of American troops in Afghanistan is doing more harm than good.
Chris Solomon, an independent from Fuquay-Varina, N.C., is among the respondents who strongly oppose the war. He said the military mission has reached the limits of its ability to help Afghans or make Americans any safer, and he would close down the war immediately.
While the rationale for the war is to fight al-Qaeda, most of the combat is against an entrenched Taliban insurgency that will outlast the foreign fighters, Solomon said. He said the conflict is reminiscent of Vietnam.
"What are we really doing there? Who are we helping?" he said in an interview.
The Associated Press-GfK Poll was conducted May 3-7 by GfK Roper Public Affairs & Corporate Communications. It involved landline and cellphone interviews with 1,004 adults nationwide and has a margin of sampling error of plus or minus 3.9 percentage points.