When a U.S. federal judge – an appointee of George W. Bush, no less – ruled in favor of marriage equality in Alabama, Judge Roy Moore didn't take it lying down. The chief justice of the state supreme court in this reddest of red states immediately blasted out this furious letter to all the state's probate courts, which issue marriage licenses, ordering that "no probate judge of the State of Alabama nor any agent or employee of any Alabama probate judge shall issue or recognize a marriage license that is inconsistent" with the state's same-sex marriage ban. Moore used even more brazen language in a separate letter to Alabama Governor Robert Bentley, cited by the Southern Poverty Law Center:

"As you know, nothing in the United States Constitution grants the federal government the authority to redefine the institution of marriage… The laws of this state have always recognized the Biblical admonition stated by our Lord… Today the destruction of that institution is upon us by federal courts using specious pretexts based on the Equal Protection, Due Process, and Full Faith and Credit Clauses of the United States Constitution… I stand with you to stop judicial tyranny and any unlawful opinions issued without constitutional authority."

This was blatantly illegal, as state courts can't overrule federal courts under the U.S. Constitution's Supremacy Clause. Nevertheless, Moore's decree led to chaos all over the state. Some probate courts ignored him and followed the federal ruling; others refused to issue marriage licenses to same-sex couples; and still others closed entirely, preventing anyone from obtaining a marriage license. (The Ku Klux Klan issued a rousing statement of support for Moore.)

This state of confusion didn't last long, as the federal court ordered Alabama's probate courts to comply with the original ruling, and most have grudgingly begun to issue licenses. It remains to be seen what penalty, if any, Moore will incur for his actions.

But this kind of insolent defiance of the law he's supposed to uphold is nothing new for Roy Moore. Infamously, in 2001, he placed a Ten Commandments monument in the Alabama state judicial building – installing it in the middle of the night, on his own private initiative, without asking anyone's permission. When a higher court found that this violated the Establishment Clause and ordered Moore to remove it, he refused. For his insubordination, he was kicked out of office, but he later ran for his old seat and won it back. (This is another demonstration of the folly of judicial elections, recently skewered by John Oliver: a judge who flouts the law and thumbs his nose at higher courts can keep getting reelected.)

However, Roy Moore is by no means the only Republican official who's been calling for defiance of the American constitutional order. Over the last few years, as they've lost some important political battles, prominent conservatives have openly advocated ignoring laws they disagree with, or even rising up in open rebellion against them.

It's no surprise that some of the wildest and most irresponsible rhetoric has come out of Texas conservatives. Almost as soon as President Obama took office, some of them were threatening to secede from the Union at the first hint that he might support policies they didn't completely agree with. Here's Governor Rick Perry in April 2009, addressing a Tea Party rally where people in the audience were shouting, "Secede!"

"We've got a great union. There's absolutely no reason to dissolve it. But if Washington continues to thumb their nose at the American people, you know, who knows what might come out of that. But Texas is a very unique place, and we're a pretty independent lot to boot."

Some Texas conservatives have taken the secessionist talk even further. Barry Smitherman, a former Republican candidate for attorney general and chairman of the state commission that regulates the oil and gas industry, has argued that Texas is "uniquely situated" to become its own country, and has claimed that he's used his regulatory position to encourage more drilling and energy production in order to prepare the state for independence.

Iowa Senator Joni Ernst, a member of the new class of extremist Republican officeholders, is another example. She's previously supported legislation that would "authorize state and local law enforcement to arrest federal officials attempting to implement the unconstitutional health care scheme known as ObamaCare." The Missouri legislature passed a similar bill to make it illegal for federal officials to enforce federal gun laws within the state, although it was vetoed by Governor Jay Nixon.

A further example is the Mormon sci-fi author Orson Scott Card. Like Roy Moore, Card is a fervent opponent of same-sex marriage – so fervent, in fact, that he's implied people should rise up and violently overthrow any government that permits it, including their own:

What these dictator-judges do not seem to understand is that their authority extends only as far as people choose to obey them.

How long before married people answer the dictators thus: Regardless of law, marriage has only one definition, and any government that attempts to change it is my mortal enemy. I will act to destroy that government and bring it down, so it can be replaced with a government that will respect and support marriage, and help me raise my children in a society where they will expect to marry in their turn.

What all these remarks – and some even more extreme – have in common is that they're invoking an idea called nullification, which asserts that individual states can render null and void any act of the federal government that they disagree with. Secession is the logical endpoint of nullification, since it holds that even a state's continued membership in the Union depends on consent that can be revoked.

The doctrine of nullification is an old and shameful idea. Throughout American history, it's been repeatedly used to defend the worst forms of bigotry and discrimination. Almost invariably, it shows up along with rhetoric of "states' rights" (which reduces to the claim that a state has the "right" to strip minorities of their rights if it wishes to). One of its earliest advocates was John C. Calhoun, a fierce defender of slavery, who was also one of the first politicians to float the idea that Southern states could secede if the rest of the country wouldn't respect their "right" to own human beings as property – an idea that, of course, was put into effect in the bloodiest and most costly of ways.

By all rights, the Union's victory in the Civil War should have put a stop to nullification talk once and for all. Yet the idea didn't die. During the civil rights era, Southern racists continued to insist that the states had the right to nullify federal acts they disliked, a claim which became the basis for massive resistance to federal voting-rights laws and court orders for desegregation. One of the most notorious proponents of nullification was the Alabama governor George Wallace, who gave an inaugural speech vowing to resist the end of Jim Crow, infamous for the line "Segregation now, segregation tomorrow, segregation forever!"

But the striking thing about Wallace's speech is how, in some respects, familiar it sounds. Except for the fact that he was defending racial segregation and not same-sex marriage bans, his rhetoric from 1963 sounds remarkably like Roy Moore's rhetoric in 2015. See for yourself:

We are faced with an idea that if a centralized government assumes enough power, enough authority over its people, that it can provide a utopian life… we find we have replaced faith with fear, and though we may give lip service to the Almighty, in reality, government has become our god. It is, therefore, a basically ungodly government and its appeal to the pseudo-intellectual and the politician is to change their status from servant of the people to master of the people, to play at being God, without faith in God and without the wisdom of God. It is a system that is the very opposite of Christ for it feeds and encourages everything degenerate and base in our people… …We intend to renew our faith as God-fearing men – not government-fearing men nor any other kind of fearing-men.

The modern-day advocates of nullification aren't chastened in the least by this historical parallel. In the last few years, they've charged ahead, proposing almost 200 bills in different states to nullify federal laws and policies they dislike: gay rights, immigration reform, health care.

While the issues may be different today, these politicians resemble the racists of old in substance as well as in tone. In both the civil rights era and the 21st century, the nullification impulse comes from the same place: the desire to preserve an unjust social order, to prevent society from becoming fairer and more equal. Then, as now, the tide of social change is rolling over conservatives who want to keep things just as they are. Nullification is their last-ditch effort to resist that change to the bitter end, to fight as long and as hard as they can against giving greater rights and protections to people whom they would prefer not to have them.