Another way to look at it: they would love to kill two birds with one stone by destroying Obama's legacy and passing a huge tax cut for the rich in one go. If they're convinced that would be hard, they could be willing to just kill *one* bird with one stone and pass the tax cut, separately.

Killing poor people isn't actually the point for them. They just don't care. If people like the Koch brothers get a huge tax cut, they don't necessarily *need* to kill poor people. And destroying Obama's legacy would be a nice partisan win for the Republicans, but it's not actually their first priority either.