I read it a little differently: when I see Sunak banging the war drum about Yemen, I think back a few years to the chaotic evacuation of Kabul.
Do you remember people in Parliament asking things like "if the Americans refuse to go back to Afghanistan, can't Britain do it alone?" I think Sunak remembers. I think he especially remembers the answer they received then - that Britain is too weak to be more than an American auxiliary, that our days of military relevance are behind us - and I think he remembers how humiliating a lot of Conservatives found that answer.
Leftists like to say that we're already against the next war. I think what we're seeing here is Sunak still not being against that last war, the return to Afghanistan that never happened, the war that exists only in the hauntology of British nationalists.