The biggest foreign policy surprise from President Biden’s first 100 days was his decision to act on a promise his predecessors hadn't: the full U.S. withdrawal from Afghanistan.

Why it matters: Biden didn't settle on an unconditional withdrawal because he saw a path to a stable Afghanistan without U.S. troops in the country. Instead, he argued that it was clear by now that no such path existed with them there.

Flashback: As Donald Trump’s May 1 deadline to pull out approached without any announcement from Biden, a delay became inevitable — likely with all the usual caveats about supporting the diplomatic process and responding to conditions on the ground.

• One Middle Eastern official told me knowingly that Biden’s challenge was to convince Americans that he was getting out and the Taliban that he was prepared to stay.

So the surprise from Biden’s mid-April announcement was not the timeline — all U.S. troops out by Sep. 11 — but how definitive it was. 

• “This is not conditions-based,” a senior administration official emphasized. No counterterrorism force would stay behind. After 20 years, America was getting out.
• Senior leaders in the Pentagon reportedly argued against that approach behind closed doors. Former top commanders, like David Petraeus, did so publicly. 
• In his speech, Biden mentioned the counterarguments — such as the U.S. would be abandoning its leverage or handing its foes a victory — and discarded them as “a recipe for keeping American troops in Afghanistan indefinitely.”