National security adviser says Joe Biden 'stands by' US withdrawal

US National Security Adviser Jake Sullivan says the failure of the Afghan military is to blame for the Taliban's swift takeover of Afghanistan.

Sullivan said Monday that President Joe Biden didn't want the US to enter a third decade of conflict in Afghanistan and believed it was time for the Afghan army to defend the country two decades after billions of dollars of investment and training by the US.

But Sullivan said, we could not give them the will and ultimately they decided that they would not fight for Kabul.

He added that the worst-case scenario for the US would be to send thousands of troops to fight in a civil war when the Afghan army wasn't prepared to fight itself."

Sullivan says Biden faced bad choices on the subject. The president ultimately opted to bring US troops home and leave the Afghans to fight for themselves.

He says it's heartbreaking to see what's happening in Kabul but that Biden stands by his decision.

Sullivan spoke Monday on ABC's Good Morning America and NBC's Today.