WASHINGTON (AP) — President Joe Biden says the Sept. 11 attacks “cannot explain” why U.S. forces should remain in Afghanistan 20 years later and that “it is time for American troops to come home” from the country's longest war.

Biden, in excerpts of a speech to the nation he plans later Wednesday, says the U.S. cannot continue to pour resources into an intractable war and expect different results. The White House released the excerpts before the afternoon address when he intends to detail his timeline for a U.S. troop withdrawal.

His plan is to pull out all the American forces — numbering 2,500 now — by this Sept. 11, according to U.S. officials, marking the 20th anniversary of the deadliest terrorist attacks against America, which were coordinated from Afghanistan. The drawdown would begin by May 1, defying the deadline for full withdrawal under a peace agreement the Trump administration reached with the Taliban last year.

“We cannot continue the cycle of extending or expanding our military presence in Afghanistan hoping to create the ideal conditions for our withdrawal, expecting a different result,” Biden says in the speech excerpts. “I am now the fourth American president to preside over an American troop presence in Afghanistan. Two Republicans. Two Democrats. I will not pass this responsibility to a fifth.”

While Biden’s decision keeps U.S. forces in Afghanistan four months longer than initially planned, it sets a firm end to two decades of war that killed more than 2,200 U.S. troops, wounded 20,000, and cost as much as $1 trillion.

Biden says he consulted with allies, military leaders, lawmakers and Vice President Kamala Harris to help make his decision to withdraw all U.S. troops by Sept. 11, two decades after the deadliest attack on American soil.

He is emphasizing that his administration will continue to support peace talks between the Afghan government and the Taliban and assist international efforts to train the Afghan military.

“It is time to end America’s longest war,” Biden says. “It is time for American troops to come home.”

He also is trying to make the case that it is time to pay more attention to greater geopolitical challenges. In the early part of his presidency, Biden has spotlighted the growing economic competition with China and malign actions by Russia targeting the United States.

“Rather than return to war with the Taliban, we have to focus on the challenges that will determine our standing and reach today and into the years to come,” Biden says, according to the excerpts.

After his speech, Biden intends to visit Section 60 of Arlington National Cemetery to honor the sacrifice of those who died in recent American conflicts.

A senior administration official said the September withdrawal date was an absolute deadline that won't be affected by security conditions in Afghanistan.

The conflict largely crippled al-Qaida and led to the death of Osama bin Laden, the architect of the Sept. 11 attacks. But an American withdrawal also risks many of the gains made in democracy, women's rights and governance, while ensuring that the Taliban, who provided al-Qaida's haven, remain strong and in control of large swaths of the country.

___ Knickmeyer reported from Oklahoma City. Associated Press writers Kathy Gannon in Islamabad and Eric Tucker in Washington and broadcast correspondent Sagar Meghani contributed to this report.