American liberty is under assault now more than at any time since the 1930s, because of runaway spending, soaring debt, ever higher taxes, proliferating regulations, implementation of Obamacare and the president’s disregard for constitutional limits on his power. Moreover, few opponents have been able to deal with his relentless class warfare.

What to do? If we reflect on some of the greatest historic movements for liberty, one thing stands out: each involved compelling moral appeals — conspicuously missing from the 2012 presidential campaign. Moral appeals tend to be about fundamental issues that can be understood by multitudes. Moral appeals evoke strong emotions capable of motivating people to support a movement for many years if necessary. Consider:

* The movement that became the war for American Independence. It began with moral outrage at high-handed British policies toward American colonists, and nobody did more than the Boston brewer Samuel Adams to incite resistance. He organized opposition to British taxes. He recruited revolutionaries by visiting shops, taverns, lodges, shipyards and volunteer fire companies. He fumed against British officials with their “ambition and lust of power above the law.” He warned that political power was “intoxicating in its nature, too intoxicating and liable to abuse.” The British governor of Massachusetts Francis Bernard denounced Adams, saying “Every tip of his pen stung like a horned snake.”

Thomas Jefferson made one of the most famous moral appeals in the second paragraph of the Declaration of Independence, asserting that human beings have natural rights no ruler could legitimately take away. Later this principle became the moral basis for the movement to achieve equal rights for women, the movement to abolish slavery and the movement to abolish compulsory racial segregation. The Declaration resonated with people around the world. The first of dozens of German translations appeared on July 9, 1776. French translations of the Declaration of Independence circulated throughout Europe, from Paris to Berlin and St. Petersburg. During the 19th century, it was translated into Chinese, Japanese, Polish, Russian, Spanish and other languages. Well into the 20thcentury, new nations issued declarations that adopted phrases from the American Declaration of Independence.

* The movement to abolish the slave trade and slavery in the Western Hemisphere. During the 1780s, Thomas Clarkson, an English preacher’s son, helped establish antislavery societies throughout Britain. He organized large public meetings that were run like religious revivals. He showed the crowds gruesome devices used to control and torture slaves, such as iron handcuffs, leg shackles, neck collars, thumb screws and branding irons, which he had acquired while researching the horrors of slavery. Clarkson also arranged for former slaves to testify about how they lost their liberty.

The British historian Thomas Babington Macaulay, in an 1825 speech, eloquently evoked moral sympathy for slaves and expressed hope for emancipation. When set free, he declared, a slave in the Caribbean “will no longer crawl in listless and trembling dejection round a plantation from whose fruits he must derive no advantage and a hut whose door yields him no protection; but when his cheerful and voluntary labor is performed, he will return with the firm step and erect brow of a British citizen from the field which is his freehold to the cottage which is his castle.”

* The movement to achieve Irish Catholic Emancipation. During the third decade of the 19th century, Daniel O’Connell led the nonviolent movement to abolish British-enforced civil disabilities on Irish Catholics — among other things, they hadn’t been permitted to own land, inherit property or vote in Parliamentary elections. O’Connell declared, “We will plant in our Native Land the Constitutional Tree of Liberty. That noble tree will flourish. Beneath its sacred shade, the People of Ireland — Catholics, Protestants and Dissenters of every Class — will sit in peace. They will see Old Ireland what she ought to be — Great, Glorious and FREE, First Flower of the Earth, first gem of the Sea.”

In an effort to promote the repeal of Ireland’s forced union with Britain, which made it easier for the British to dominate the Irish, O’Connell held a series of “Monster Meetings” during the early 1840s. Some of these reportedly drew crowds exceeding 300,000 people. Since not everybody could hear O’Connell’s moral outrage at the British, relay speakers repeated his words for people farther and farther away. Although his health was fading, and he wasn’t able to repeal the union, he showed how passionate moral appeals could motivate large numbers of people. Later generations picked up where he left off, and Ireland achieved independence.

* The movement to abolish American slavery. Nobody blasted immoral slavery like William Lloyd Garrison who launched the American abolitionist movement. “What has brought our country to the verge of ruin?” he scowled. “THE ACCURSED SYSTEM OF SLAVERY! To sustain that system, there is a general willingness to destroy LIBERTY OF SPEECH and of the PRESS, and to mob or murder all who oppose it. Every principle of justice, every axiom of liberty, every feeling of humanity, all the fundamental axioms of republican government are derided and violated.”

Unlike many reformers who know what they’re against but don’t think through what they’re for, Garrison had an exhilarating moral vision — natural rights. “Black children,” he declared in 1829, “possess the same inherent and unalienable rights as ours.” He frequently cited the Declaration of Independence. He crusaded for women’s rights and peace. He defended persecuted Chinese immigrants. And he wrote: “I avow myself to be a radical free trader, even to the extent of desiring the abolition of all custom-houses throughout the world.”

* The British movement for free trade.  The case for free trade had been made mainly with economic arguments about how consumers benefited when they’re free to buy from anyone they choose, including foreign suppliers often kept out of markets by trade restrictions. Then came the British textile manufacturer Richard Cobden who, in 1838, envisioned a movement for free trade. “It appears to me,” Cobden wrote an Edinburgh publisher, “that a moral and even a religious spirit may be infused into that topic [free trade], and if agitated in the same manner that the question of slavery has been, it will be irresistible.”

Cobden’s moral appeals became especially compelling after the 1845 failure of the Irish potato crop that led to massive starvation. Biographer John Morley reported that Cobden “knew of a place where a hundred wedding-rings had been pawned in a single week to provide bread; and another place where men and women subsisted on boiled nettles, and dug up the decayed carcass of a cow rather than perish of hunger.”

* The American movement to achieve equal rights for women. In 1848, upstate New York housewife Elizabeth Cady Stanton began leading the movement to secure equal rights. She wrote A Declaration of Rights and Sentiments which, borrowing some of Thomas Jefferson’s words in the Declaration of Independence, made a moral case for equal rights: “We hold these truths to be self-evident: that all men and women are created equal; that they are endowed by their Creator with certain inalienable rights; that among these are life, liberty, and the pursuit of happiness; that to secure these rights governments are instituted, deriving their just powers from the consent of the governed. Whenever any form of government becomes destructive of these ends, it is the right of those who suffer from it to refuse allegiance to it.”

Then Stanton issued a moral indictment: “The history of mankind is a history of repeated injuries and usurpations on the part of man toward woman. He has never permitted her to exercise her inalienable right to the elective franchise. He has withheld from her rights which are given to the most ignorant and degraded men—both natives and foreigners. He has made her, if married, in the eye of the law, civilly dead. He has taken from her all right in property, even the wages she earns. In the covenant of marriage, she is compelled to promise obedience to her husband, and he becomes, for all intents and purposes, her master—the law giving him power to deprive her of her liberty and to administer chastisement.”

* The American civil rights movement. Rev. Martin Luther King made moral appeals as he led nonviolent protests against compulsory racial segregation. In 1963, while in a Birmingham jail, he explained that “An unjust law is a code that a majority inflicts on a minority and is not binding on itself. An unjust law is a code inflicted upon a minority which the minority had no part in enacting, because they did not have the unhampered right to vote. We can never forget that everything Hitler did in Germany was ‘legal,’ and everything the [1956 anticommunist] freedom fighters did in Hungary was ‘illegal.’ ”

Rev. King inspired people with his fearless devotion. He was jailed 14 times, he was the target of countless death threats, he was stoned, he was stabbed, his home was blasted by a shotgun, his home was bombed, and a motel room where he stayed was bombed, too, before he was assassinated.

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In recent times, Ronald Reagan stood out as a rare leader who could express moral appeals for liberty. He said, for instance, “Only when the human spirit is allowed to invent and create, only when individuals have a personal stake in their success — only then can societies remain dynamic, prosperous and free.” Reagan knew how to deal with class warfare, too: “Since when do we in America believe that our society is made up of two diametrically opposed classes—one rich, one poor—both in a permanent state of conflict and neither able to get ahead except at the expense of the other? Since when do we in America accept this alien, discredited theory of social and class warfare? Since when do we in America endorse the politics of envy?”

Reagan made defending liberty look easy, but he had been speaking, writing and debating for some three decades before his 1980 White House run — a clue, perhaps, that expressing moral appeals isn’t a skill that a political leader is likely to master in campaign cramming sessions.

We need to rediscover compelling moral appeals for liberty that made the world a better place — so they could help do it again.