Last week, following the murder of six people and the attempted murder of Rep. Gabrielle Giffords in Arizona, the American people were given a vivid display of the single most important tactic of the Left: libeling opponents.

Most Americans have been naively and blissfully unaware of this aspect of the Left’s arsenal against the Right. But now, just as more Americans than ever before understand the Left’s limitless appetite for political power in an ever-expanding state, more Americans than ever before understand that a key to the Left’s success is defaming the Right.

I do not recall any major American daily attacking another major American daily the way the Wall Street Journal attacked the New York Times last week under the heading “The New York Times has crossed a moral line.” I do not recall Pulitzer Prize-winning Washington Post columnist Charles Krauthammer ever expressing contempt toward a colleague the way he did against New York Times columnist Paul Krugman last week. Krauthammer ended his column “Massacre, Followed by Libel,” with this sentence: “The origins of Loughner’s delusions are clear: mental illness. What are the origins of Krugman’s?”

People are awakening to the crucial fact of left-wing success: The only way the Left can succeed in America is by libeling the Right. Only 20 percent of Americans label themselves liberal, let alone leftist. How, then, do leftists get elected? And why don’t more Americans call themselves conservative, when, in fact, so many share conservatives’ values?

The answer to both questions is that, through its dominance of the news media, entertainment media, and educational institutions, the Left has been able to successfully demonize the Right for at least half a century.

The Left rarely convinces Americans to adopt its views. What it does is create a fear of the Right that influences many Americans to align themselves with the Left.

For example, most Americans want to retain the man-woman definition of marriage. Even most voters in liberal Californians want to. The Left has not been able to convince even Californians to redefine marriage to include members of the same sex. So what the Left did was to declare as “haters” all those who wanted California to retain the definition of marriage as uniting a man and a woman. Prop 8 became “Prop Hate.”

But the Left’s modus operandi was never as apparent as it was this past week when it took a tragic mass killing of innocents by a violent, mentally ill individual and transformed it — within hours — into an attack on the decency of the Right — specifically Sarah Palin, the Tea Party, FoxNews, and talk radio.

The same Left, led by the New York Times, that warned against making any quick assumptions that Islam had played any role in Maj. Nidal Hassan’s murder of 13 people and wounding of 30 others at Fort Hood, immediately declared that the Arizona murders were largely a result of a “climate of hate” induced by Sarah Palin and other conservatives.

It wasn’t true. They knew it wasn’t true. And, yes, it was a libel.

But when you control all the major news media, Hollywood, much of rest of the culture, and most of the high schools and colleges, how are most people supposed to realize that?

What makes last week different is this: The Left, for the first time, does not have the same monopoly over mass information and the Republican Party is no longer emasculated. There is talk radio, there is the internet, there is FoxNews, and there is a vigorous, conservative Republican Party. So, when the Left unleashed its libel against the Right, claiming that it was responsible for a “climate of hate” that produced Jared Loughner, to its shock, America did not lie down and believe it. Many millions did, as usual. But for those with eyes to see, it was a false accusation, and for many, for the first time, it provided a clear view into how the Left operates.

As it becomes ever more obvious that Loughner’s crimes had nothing — absolutely nothing — to do with conservatives, the Left will do three things: change the subject by criticizing Sarah Palin’s use of the term “blood libel” (a term whose use by Palin was honorably defended by Prof. Alan Dershowitz, a prominent Jewish liberal); deny it ever really blamed the Right for the Loughner’s crimes (hoping, with good reason, that Americans have a short memory); and continue to blame the Right for creating the “climate of hate” that the Left itself has created.

That is why it is important for conservatives and honorable liberals not to allow Americans to forget what the Left did last week. It is the key to giving conservatives the good name they deserve. And it is the key to giving the Left the name it deserves.

— Dennis Prager is a nationally syndicated radio talk-show host and columnist. He may be contacted through his website, dennisprager.com.