Also, the loophole found by the Federal government involving withholding funds from states if their will isn't met. They can't tell the states to, say, set a maximum speed limit [0] or force annual standardized testing [1]. But they can withhold highway and education funds if the states don't. I feel like this has pretty dramatically increased the intended power of the federal government over the states, but no one ever talks about it.

[0] https://en.wikipedia.org/wiki/National_Maximum_Speed_Law

[1] https://en.wikipedia.org/wiki/No_Child_Left_Behind_Act