Chump threatens to withhold federal funds from sanctuary cities and states. Is there a precedent or means for those threatened to withhold the very funds collected via various sales taxes?
Not funds collected as sales taxes because those are state taxes and completely within the jurisdiction of the states themselves. But states rely on all sorts of distributions to them of federal funds (based on federal taxes), and presumably these would be what Trump might try to use as leverage. There are precedents for federal funds to be denied to states when they refuse to abide by federal laws governing programs administered by states and receiving federal funds for doing so. Trump could so manage laws with his Republican majorities (plus perhaps a compliant Supreme Court) to make good his threats. He might have to use another excuse - some other trumped (sic) up issues - instead of sanctuary.