An Associated Press analysis found that about four-fifths of the states now have enacted local laws that directly reject or ignore federal laws on marijuana use, gun control, health insurance requirements and identification standards for driver's licenses. The recent trend began in Democratic leaning California with a 1996 medical marijuana law and has proliferated lately in Republican strongholds like Kansas, where Gov. Sam Brownback this spring became the first to sign a measure threatening felony charges against federal agents who enforce certain firearms laws in his state.
Some states, such as Montana and Arizona, have said "no" to the feds again and again - passing states' rights measures on all four subjects examined by the AP - despite questions about whether their "no" carries any legal significance.
"It seems that there has been an uptick in nullification efforts from both the left and the right," said Adam Winkler, a professor at the University of California at Los Angeles who specializes in constitutional law.
Yet "the law is clear - the supremacy clause (of the U.S. Constitution) says specifically that the federal laws are supreme over contrary state laws, even if the state doesn't like those laws," Winkler added.
The fact that U.S. courts have repeatedly upheld federal laws over conflicting state ones hasn't stopped some states from flouting those federal laws - sometimes successfully.
About 20 states now have medical marijuana laws allowing people to use pot to treat chronic pain and other ailments - despite a federal law that still criminalizes marijuana distribution and possession. Ceding ground to the states, President Barack Obama's administration has made it known to federal prosecutors that it wasn't worth their time to target those people.
Federal authorities have repeatedly delayed implementation of the 2005 Real ID Act, an anti-terrorism law that set stringent requirements for photo identification cards to be used to board commercial flights or enter federal buildings. The law has been stymied, in part, because about half the state legislatures have opposed its implementation, according to the National Conference of State Legislatures.
About 20 states have enacted measures challenging Obama's 2010 health care laws, many of which specifically reject the provision mandating that most people have health insurance or face tax penalties beginning in 2014.