This article in the New York Times has some interesting background on this: specifically, it goes into some detail about Alabama's long history of defying the federal government over all sorts of things; it's pretty much a hangover from the Civil War, the remnant of that diehard insistence on "states' rights."
Such brazen and often futile campaigns are practically hard-wired into the state's character. Long after George Wallace's stand against integration in the schoolhouse door, to which Chief Justice Moore's stance has been inevitably compared, the state's record of taking on the federal government in long-shot battles has continued to set it apart even from its conservative neighbors.
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"It's like our oxygen is defiance and our identity is aggrievement," said Diane McWhorter, an Alabama native and author of the Pulitzer Prize-winning book about civil rights-era Birmingham, "Carry Me Home."That history is another reason why it would be far better for the feds to sit this one out, at least for the time being. It seems to me that changing that pattern of defiance is a better goal than "punishing" the state for its actions, which is how any federal intervention would be seen. One way to get people, and perhaps states, to change bad behavior is
to make them clean up their own messes. If Justice Moore is disciplined by the state's judicial ethics board, he won't be nearly the martyr/hero he'd be if the feds stepped in and cited him for contempt or arrested him.
Let the rulings on this and other civil rights matters come from federal courts, but give the state the chance to pick up the burden of forcing compliance with those rulings; if the people of Alabama see that they just end up having to fix the messes their leaders make, while looking foolish until they do, they'll likely have a lot less tolerance for the folks who make them.