> there's a doctrine they can't force the states to act to enforce a federal law, but also the states can't countermand the federal law, there's a whole history of courts dealing with the interactions.

The Fugitive Slave Acts were two of these conflicts. The first one overruled any state that offered sanctuary while also making it a federal crime to assist runaways. The second one aggravated tensions between slave states and the rest of America. Under the Fugitive Slave Act of 1850, it was not legal for a suspected runaway slave to deny being the slave described in the paperwork. States were required to assist slave catchers. Also, suspected runaway slaves were not permitted any sort of trial. It legalized kidnapping any black person who vaguely fit the description on the paperwork.

https://en.wikipedia.org/wiki/Fugitive_Slave_Act_of_1850

Prior to the Commodities Futures Modernization Act of 2000, some states regulated credit default swaps as insurance products while some state's statutes said that CDS were gambling (and outlawed it completely). The CFMA overruled the states that had outlawed CDS. This was one of the major causes of the 2007/2008 financial meltdown.

https://en.wikipedia.org/wiki/Commodity_Futures_Modernizatio...