I don't think Joe Manchin is stupid. I think he's often craven, and uses his demands as a cover for the fact that he's a hardcore Koch conservative (don't forget, he's a co-founder of the No Labels caucus), and that requires him to come up with rationales, no matter how little sense they make. Last week, he stamped his feet and demanded Biden cut his key climate change plans, and now he demands that Dems put a $60K income cap on the child tax credit instead of $150K, and add a work requirement.