Because they convince themselves that it's not a human child until birth.From the end of the letter:
“Even if this was not so, we would remind you that no one’s political survival is more important than the survival of our children.”
Which is why abortion is the medical standard of the Democrat party?
I’m convinced that many Democrats are not human, even when they act like children.
This is simple, their fake impeachment is going nowhere, they can't stop Trump from being reelected. They know if they could coerce Trump into this then he's done.