It is clear that Trump was led into his stance because a few seconds before ordering her firing, he literally asks which ambassador?
pbs.org/newshour/natio…
"How long will [Ukraine] last in a fight with Russia?" Trump asks.
"Without us, not very long," a voice says.
"Without us," Trump says.
A voice says Ukraine is part of pipelines in Europe.
Trump appears to ask, “Ukraine has oil?”
Someone says, "Yes."
Trump asks, “Why aren’t companies going in? Too risky?” Someone says, “Exactly."
About 6 mins into this recording, Pres Trump says, "This is all sort of like off the record right?" A voice says, "Yes."
So we have Igor Fruman recording the president, that recording now made public and Trump unaware that his words will later be heard around the world.