from his Bloomberg column:

What really worries Harkin and his allies is that a bill funding the new approaches will draw support away from Harkin’s own bill — leaving Bush’s rule firmly in place.
A good example is Senator Johnny Isakson, a Georgia Republican. He had long been counted as a Harkin supporter. Last week he wavered.
“If there’s a way to get stem cells without destroying an embryo,” he told Roll Call, “then that is where (the federal government) should be making their investment, because the ethical and moral issues go away.”
It sounds like a suitable compromise…