(CNN) President Donald Trump's administration is preparing to announce a reduction of US troops from Afghanistan amid a diplomatic push to renew peace talks with the Taliban, a senior administration official confirmed to CNN.

It's not exactly a surprise move: Trump has already signaled publicly that he intends to drawdown several thousand troops from the country. But the latest effort to wind down US military involvement there comes at a time of intense reflection in Washington about what, exactly, has been accomplished by an 18-year experiment in nation-building there.

The raw numbers speak for themselves. Since 2001, the United States has spent nearly $133 billion on the reconstruction of Afghanistan , a figure that is a fraction of the estimated $2 trillion that US military operations have cost

A high price paid

The human cost has also been high. Approximately 2,300 US troops have been killed in Afghanistan, and the price paid by Afghans has been far higher: Over 58,000 Afghan soldiers and police have been killed in the conflict, along with 38,000 civilians. An estimated 42,000 anti-government insurgents were killed.

But that massive expenditure has yielded little that can be declared as a clear victory. The US Agency for International Development can point to the over 3.5 million Afghan girls who have been enrolled in school as one metric of success, or the over 1,200 miles of new highway that have been built, including the ring road that connects many of the country's rural provinces. Kabul now has a nascent middle class and local media that enjoy a degree of press freedom that's unthinkable in neighboring countries.

But the central government in Kabul remains in a precarious position. The Taliban -- ousted from power by a US-led campaign that combined precision bombing and the insertion of special-operations troops and CIA operatives in 2001 -- have staged a dramatic comeback, strengthening their control over more of the country's districts. Afghan government forces are bearing the brunt of heavy fighting.

And the publication of a major new investigation by the Washington Post has raised larger questions about the long-term goals of US strategy there -- and whether US political and military leaders have leveled with the public about Afghanistan's lack of progress.

Drawing on a document trove called the Afghanistan Papers , the Post shed new light on failed efforts to police and secure Afghanistan, combat the massive opium trade, and build a functioning state.

The Afghan government's ineptitude and corruption is well documented, as is US support for questionable local warlords. But documents, including "lessons learned" interviews conducted by the Special Inspector General for Afghanistan Reconstruction, a congressionally mandated oversight body established to track and account for the billions spent there, show that US diplomatic and military officials consistently painted overly-rosy assessments of Afghan progress.

The parallels with the Vietnam War-era Pentagon Papers are clear: Then, as now, US officials consistently gave inflated assessments of a beleaguered government's ability to fight independently of US aid.

Collapse is feared

Part of the problem was the can-do attitude of the US military: The military took on a nation-building mission that was far beyond the scope of its original task: Toppling the Taliban and denying safe haven to al Qaeda. The US also knew very little about the country, its complex ethnic makeup, or the histories of key local players.

And experts warn that a US drawdown could precipitate a collapse of the central government. The Soviet backed-government of Mohammad Najibullah, for instance, held out against mujahideen fighters for around three years after the Soviet withdrawal. Once the USSR collapsed and aid from Moscow dried up, his government quickly fell.

A senior administration official confirmed to CNN that the US plans to withdraw about 4,000 troops from Afghanistan -- roughly a third of the 12,000 to 13,000-strong force currently on the ground there. But the drawdown of US forces has long been underway.

Just over a decade ago -- on December 1, 2009 -- President Barack Obama announced a surge in troops that would bring the US presence in Afghanistan to 100,000 by mid-2010. Afghanistan at the time was depicted as a just conflict that had been neglected in the wake of President George W. Bush's disastrous decision to go to war against Iraq in 2003.

In reality, both the wars in Iraq and Afghanistan began as regime-change operations, and then morphed into more open-ended missions. And ending those wars has proven far more difficult than beginning them.

As 2019 draws to a close, the US has been redoubling efforts to return to the peace table with the Taliban.

Last week, US Special Representative for Afghanistan Reconciliation Ambassador Zalmay Khalilzad visited Islamabad to discuss the current status of US-Taliban talks, explaining that talks in Doha with Taliban negotiators were on a "brief pause" to allow the Taliban to consult with their leadership about the need for them to "show they are willing & able to respond to Afghan desire for peace."

It's worth recalling here that those talks are restarting after an about-face by Trump himself. In September, Trump unexpectedly called off formal talks after a Taliban-claimed attack in Kabul killed a dozen people, including a US soldier. But on a surprise Thanksgiving visit to troops in Afghanistan, Trump offered another reveal: peace talks with the Taliban had restarted.

Trump may not have started the war, but he may end up owning a good part of its legacy.