America’s top diplomat appeared on political TV shows on Sunday to defend the US’s mission in Afghanistan and attempt to hold back a tide of comparisons between the chaotic scenes unfolding in Kabul, where the Taliban is now poised to retake power, and the humiliating fall of Saigon 46 years ago.

“This is manifestly not Saigon,” the US secretary of state Antony Blinken told ABC’s This Week. “We went into Afghanistan 20 years ago with one mission in mind, and that was to deal with the people who attacked us on 9/11, and that mission has been successful.”

Blinken’s rejection of any parallels with the iconic image of helicopters evacuating personnel from the US embassy in Saigon in April 1975 at the end of the Vietnam war came as the skies over the Afghan capital were filled with Chinooks and Black Hawks ferrying US embassy staff to a secure location at the international airport. The secretary of state made his remarks with Taliban forces amassing inside the capital, and with their representatives already negotiating a “peaceful transfer” of power at the presidential palace.

With the Biden administration increasingly on the defensive over the Taliban’s stunningly rapid sweep across the country, Blinken attempted to justify the rout by arguing that the US mission in Afghanistan was accomplished and that retaining forces in the country was not an option. “Al-Qaida has been vastly diminished, and its capacity to attack us again from Afghanistan right now does not exist,” he said.

To have kept a military presence in Afghanistan beyond the 1 May deadline set by the previous Trump administration would have been to invite a revival of Taliban attacks on US personnel, Blinken said. “In that instance I would be having to explain why we were sending tens of thousands of forces back into Afghanistan to continue a war that the country needs to end after 20 years.”

But the unseemly scramble to evacuate the embassy staff, coupled with the redeployment of 6,000 US troops to the country in a reversal of the withdrawal effectively completed just weeks ago, has left the White House facing accusations that it has botched the US departure with potentially long-term consequences. Concern is also rising for the more than 18,000 Afghans and their families who worked for the US as translators and in other capacities who are at risk of Taliban reprisals.

On Sunday morning a briefing by senior Biden administration officials for Congressional leaders grew acrimonious. Kevin McCarthy, the leader of the Republicans in the House of Representatives, exploded in anger, calling the withdrawal an “embarrassment”, according to Politico.

McCarthy said “I have passion and I have anger”, and asked “Are we secure at home over the coming weeks?” His outburst came during an almost hour-long call with Blinken, the secretary of defense Lloyd Austin and chairman of the joint chiefs of staff Mark Milley.

Nancy Pelosi, the Democratic leader in the House, also spoke, thanking Biden for his “clarity of purposes” but raising concerns about the future of women in Afghanistan, Politico reported.

The potent analogy with Saigon, one of the most ignominious episodes in the US’s long history of foreign interventions, is increasingly being held against Biden personally. When asked in July whether there was substance to the Vietnam comparison, the president replied: “None whatsoever. Zero… There’s going to be no circumstance where you see people being lifted off the roof of an embassy of the United States from Afghanistan.”

Opinion polls suggest that after almost 20 years of war, with more than 2,000 US military deaths and $1tn spent in a failed effort to build a solid Afghan government and fighting force capable of resisting the Taliban, the American people have had enough. A poll last week by the Chicago Council on Global Affairs found that 70% of those surveyed supported the decision to withdraw US troops.

On Saturday Biden echoed the sentiment reflected in opinion polls by saying that “an endless American presence in the middle of another country’s civil conflict was not acceptable to me”.

He added that he was the fourth president to preside over US troops in Afghanistan – two from either main political party – and that “I would not, and will not, pass this war onto a fifth”.

Even though the plan for withdrawal was forged by the previous Trump administration in negotiations with the Taliban in Doha, Qatar, in February 2020, Republican leaders are holding nothing back in their criticisms of the current White House.

Michael McCaul, the top foreign affairs Republican in the House of Representatives, described the events in Kabul as “an unmitigated disaster of epic proportions” and said Biden “is going to have blood on his hands”.

Speaking on CNN’s State of the Union, McCaul said that the Biden team “totally blew this one. They completely underestimated the strength of the Taliban and they didn’t listen to the intelligence community.”

Ridiculing Biden’s claim that the Afghan withdrawal bore no comparison with Vietnam, McCaul said: “We think it’s going to be worse than Saigon. When they raise the black flag of the Taliban over our United States embassy – think of that visual.”