You’re not wrong. Trump had already set things in motion and if Biden would have reversed it, tens of thousands of additional troops would have had to return to Afghanistan which was politically impossible. People blaming Biden either have short memories or don’t realise that Trump effectively signed a surrender deal with the Taliban, thereby abandoning the Afghan government which fell even before the withdrawal was complete.
As well as abandoning allies in Afghanistan he also abandoned the Kurds in Syria. Abandoning allies to score a few cheap political points is fairly routine for Trump and not enough was made of it at the time. He’s also trying his best to get Ukraine to surrender to Russia and his commitment to NATO is open to question.