Former Defense Secretary Mark Esper said Tuesday that he was concerned that then-President Donald Trump "undermined" the US" 2020 agreement with the Taliban by pushing for US forces to leave Afghanistan without the Taliban meeting the conditions of the deal. The Trump administration"s "Agreement for Bringing Peace to Afghanistan" outlined a series of commitments from the US and the Taliban related to troop levels, counterterrorism and intra-Afghan dialogue aimed at bringing about "a permanent and comprehensive ceasefire." But, Esper told CNN"s Christiane Amanpour, "my concern was that President Trump, by continuing to want to withdraw American forces out of Afghanistan, undermined the agreement, which is why in the fall when he was calling for a return of US forces by Christmas, I objected and formally wrote a letter to him, a memo based on recommendations from the military chain of command and my senior civilian leadership that we not go further — that we not reduce below 4,500 troops unless and until conditions were met by the Taliban." "Otherwise," Esper continued, "we would see a number of things play out, which are unfolding right now in many ways." Trump fired Esper in November 2020 in the wake of the presidential election. The agreement between the Taliban and the US has come under fresh scrutiny in recent days after Afghanistan"s civilian government in Kabul fell to Taliban fighters this weekend, almost two decades after they were driven from the city by US troops. After years of negotiations, the Taliban and the Trump administration finally signed a peace deal in 2020. The US agreed to withdraw troops and release some 5,000 Taliban prisoners, while the Taliban agreed to take steps to prevent any group or individual, including Al Qaeda, from using Afghanistan to threaten the security of the US or its allies. But the deal didn"t bring about peace. Following the agreement, violence in Afghanistan grew to its highest levels in two decades and the Taliban increased their control of wider swaths of the country. By June of this year, the Taliban contested or controlled an estimated 50% to 70% of Afghan territory outside of urban centers, according to a United Nations Security Council report. Although Afghan security forces were well funded and well equipped, they put up little resistance as Taliban militants seized much of the country following the withdrawal of US troops beginning in early July. Now factions within the Biden administration are embroiled in a blame game over why the US government didn"t act sooner to withdraw American citizens and Afghans who helped the US over two decades of war, leading to a rushed and dangerous evacuation. In his first public comments since the Taliban solidified control of Kabul, President Joe Biden on Monday laid blame on the Afghan security forces" unwillingness to fight and the decisions of previous administrations — including the Trump administration — while failing to directly address the chaos unfolding on his watch. Biden conceded that the Taliban takeover happened faster than anticipated, though he said he stands "squarely behind" his decision. — CNN