So my take on Trump and Operation Warp Speed. It's a calculated move he had to make. Similar to a chess move.
If he doesn't push to accelerate the vax, what is the option? Extended lockdowns. By having the vax ready sooner, he then pushes for everything to open up and return to normal. He took that move away from the DS. And he's always said it should be optional, not mandatory.
The quote about saving 100M lives I feel applies to this, not the vax. The lockdowns would have been much worse and more catastrophic.
On his position to stand by the vax recently. Not sure. But my guess is he's holding this line till other heads of state begin to question. If he starts to question it now, they'll blame him for it. When the narrative fully changes, he'll say he was duped by his advisors.