The Pew Research Center poll found a record 56 percent of Americans now favor the 100,000 US forces currently stationed in Afghanistan be brought home as quickly as possible.

Obama has made his final decision on the scale and scope of the withdrawal and will announce it in a speech from the White House 8 p.m. EDT (midnight GMT) on Wednesday.

The president must campaign on his war record as he seeks re-election next year. But popular backing for the mission has slipped in the face of mounting human and financial costs, at a time of tight budgets and high unemployment back home.

This was the first time a majority of Americans had backed a fast withdrawal and compared with 40 percent a year ago.

In contrast, just 39 percent want US troops to stay in Afghanistan until the situation had stabilized, which was down sharply from 53 percent who felt that way a year ago.

“Over the past year, support for removing US troops from Afghanistan as soon as possible has increased across nearly all political and demographic groups,” the Pew Research Center said in a statement.

It found two-thirds of Democrats and 57 percent of independents now immediate troop withdrawal, while the number of Republicans who favor getting US forces out has jumped to 43 percent from 31 percent a year ago.

The survey comes as other polls show a dip in Obama’s approval ratings that has erased the bump in popularity that he recorded after US commandos killed Al-Qaeda leader Osama Bin Laden in Pakistan on May 2.

Gallup said that Obama’s approval rating was back at 46 percent after averaging around 50 percent last month.