How can we account for our present situation unless we believe that men high in this Government are concerting to deliver us to disaster? This must be the product of a great conspiracy, a conspiracy on a scale so immense as to dwarf any previous such venture in the history of man. A conspiracy of infamy so black that, when it is finally exposed, its principals shall be forever deserving of the maledictions of all honest men.

Who constitutes the highest circles of this conspiracy? About that we cannot be sure. We are convinced that Dean Acheson, who steadfastly serves the interests of nations other than his own, the friend of Alger Hiss, who supported him in his hour of retribution, who contributed to his defense fund, must be high on the roster. The President? He is their captive

It was Marshall, with Acheson and Vincent eagerly assisting, who created the China policy which, destroying China, robbed us of a great and friendly ally, a buffer against the Soviet imperialism with which we are now at war.

It was Marshall who, after long conferences with Acheson and Vincent, went to China to execute the criminal folly of the disastrous Marshall mission.

It was Marshall who, upon returning from a diplomatic defeat for the United States at Moscow, besought the reinstatement of forty millions in lend-lease for Russia.
[...]
It is Marshall-Acheson strategy for Europe to build the defense of Europe solely around the Atlantic Pact nations, excluding the two great wells of anti-Communist manpower in Western Germany and Spain and spurning the organized armies of Greece and Turkey-another case of following the Lattimore advice of "let them fall but don't let it appear that we pushed them."

It is Marshall who, advocating timidity as a policy so as not to annoy the forces of Soviet imperialism in Asia, had admittedly put a brake on the preparations to fight, rationalizing his reluctance on the ground that the people are fickle and if war does not come, will hold him to account for excessive zeal.

What can be made of this unbroken series of decisions and acts contributing to the strategy of defeat? They cannot be attributed to incompetence. If Marshall were merely stupid, the laws of probability would dictate that part of his decisions would serve this country's interest. If Marshall is innocent of guilty intention, how could he be trusted to guide the defense of this country further? We have declined so precipitously in relation to the Soviet Union in the last 6 years. How much swifter may be our fall into disaster with Marshall at the helm? Where Will all this stop? That is not a rhetorical question: Ours is not a rhetorical danger. Where next will Marshall carry us? It is useless to suppose that his nominal superior will ask him to resign. He cannot even dispense with Acheson.

What is the objective of the great conspiracy? I think it is clear from what has occurred and is now occurring: to diminish the United States in world affairs, to weaken us militarily, to confuse our spirit with talk of surrender in the Far East and to impair our will to resist evil. To what end? To the end that we shall be contained, frustrated and finally: fall victim to Soviet intrigue from within and Russian military might from without. Is that farfetched? There have been many examples in history of rich and powerful states which have been corrupted from within, enfeebled and deceived until they were unable to resist aggression. . . .

It is the great crime of the Truman administration that it has refused to undertake the job of ferreting the enemy from its ranks. I once puzzled over that refusal. The President, I said, is a loyal American; why does he not lead in this enterprise? I think that I know why he does not. The President is not master in his own house. Those who are master there not only have a desire to protect the sappers and miners - they could not do otherwise. They themselves are not free. They belong to a larger conspiracy, the world-wide web of which has been spun from Moscow.

The time has come to halt this tepid, milk-and-water acquiescence which a discredited administration, ruled by disloyalty, sends down to us. The American may belong to an old culture, he may be beset by enemies here and abroad, he may be distracted by the many words of counsel that assail him by day and night, but he is nobody's fool. The time has come for us to realize that the people who sent us here expect more than time-serving from us. The American who has never known defeat in war, does not expect to be again sold down the river in Asia. He does not want that kind of betrayal. He has had betrayal enough. He has never failed to fight for his liberties since George Washington rode to Boston in 1775 to put himself at the head of a band of rebels unversed in war. He is fighting tonight, fighting gloriously in a war on a distant American frontier made inglorious by the men he can no longer trust at the head of our affairs.

The America that I know, and that other Senators know, this vast and teeming and beautiful land, this hopeful society where the poor share the table of the rich as never before in history, where men of all colors, of all faiths, are brothers as never before in history, where great deeds have been done and great deeds are yet to do, that America deserves to be led not to humiliation or defeat, but to victory.

And that's McCarthyism in all its insane glory.  Just think of how detached from reality one would have to be to argue that Acheson and Marshall - the creators of the Cold War alliance system, of the eponymous Marshall Plan, the ruthless enforcers of containment - the architects of America's eventual victory in the Cold War, were Soviet agents.  There are echoes of it today in the venom directed against the critics of the Iraq war, though no accusations of active collaboration with America's enemies - just of being 'useful idiots' as they used to say.  There are strong echoes of the expansion of the domestic security apparatus to root out enemies and faint ones of the witchhunts.

There are also attempts to rehabilitate McCarthyism using several arguments. First that a few of the people targetted genuinely were traitors, spies for the Soviet Union, somehow the damage to thousands of innocent people doesn't matter. Secondly that Communists were in effect supporting an utterly evil system - no argument there, but they were a tiny minority who couldn't pose a threat since that fact was obvious to the vast majority of Americans.  

McCarthyism is actually a perfect illustration of how a political ideology of extremism and paranoia can pose a greater threat to America than a much worse but less powerful ideology.  Today the evil ideology from abroad is violent radical Islam. It is much weaker than Communism was - no superpower Al Qaeda state and it is virtually non existent in the US. The overreaction hasn't gone as far either. But the folks currently in power are the ideological descendants of McCarthyism both in its domestic paranoia and the 1950's right's penchant for dangerous aggression abroad.