For example, if we ever had a president that got elected based on a promise of "we're going to put in place an assault weapons ban, and use the ATF to enforce it", cities wouldn't be allowed to simply ignore it and call themselves a "2A sanctuary", and then have a bunch of protestors getting into physical confrontations with ATF agents when they're on their way to enforce it.
If they were smart, they'd cooperate.
The did cooperate during the first 6-7 years of Obama's tenure, and ICE operations were going much more smoothly when they were taking custody of people from county jails and city holding cells as opposed to trying to do it at Home Depot.
Anti-immigration protesters and federal agents again clashed Sunday night outside a hotel near the University of Minnesota campus in Minneapolis.
kstp.com
"We heard some ICE agents were staying at this hotel, so let's go bust up the place and start some stuff"
We know that a certain percentage of these types of encounters will lead to physical escalation, and we know a subset of those will lead to force being used.