If a parasite takes enough energy from its host, the host will die. Most parasites, like intestinal worms, fleas, ticks, and etc. limit their demands on the host so that the host can survive. Governments don't seem to have that much sense.
Governments quite regularly take so much energy from the societies in which they are embedded that the societies collapse into chaos. The good news is that over time government, as we know it today will disappear. The bad news is that anyone who presently lives under the yoke of a government can expect it to become worse and worse until the society collapses.
Our rules of jurisprudence are a mechanism that limits the power of the state and provides for the survival of both the state and the society in which it is embedded. These mechanisms include the right to a trial by jury, the right to assemble, freedom of speech, freedom from cruel and unusual punishment, freedom from excessive taxation, and the right to vote. These rights all protect the state from itself as much as they protect the citizens. Mechanisms such as this exist in any society. They may be very different from the western tradition. But they all erode over time. That erosion is certainly well documented in the United States of 2004. No government has ever been stable for more than a few hundred years and it looks like unusually long period of stability of the United States is nearing its end. It also seems there are many countries in the world, which are in similar situations.
The manager of a government unit has the same problem as the leader of any other criminal enterprise. How can he perform the criminal acts he routinely uses to turn a profit without himself becoming the victim of other criminals or being done in by organized resistance from his victims? The solution is the same for presidents or mafia dons. He must convince a large segment of the affected population that he does them more good than harm. Both governments and organized crime figures are remarkably successful at this propaganda enterprise. But modern means of processing and disseminating information may be changing that. Slick Willy Clinton wasn't doing anything many of his predecessors hadn't done with Monica, and GW Bush was far from the first president to lie the USA into war. Both got caught because of modern technology.
Technology is going to be even more of a problem for future presidents. The ordinary citizen is often caught between criminal gangs, the government and organized crime. Then the citizen ends up paying for the support of both. More and more people are realizing that force and fraud cause just as much damage to society, no matter whether the perpetrators come equipped with uniforms and paperwork
In an interconnected world, governments have an unfortunate tendency to march in lockstep towards disasters like World War One, the Great Depression of the 1930s and World War Two. Gradually, taxation increases, regulations increase, the underground economy expands. More and more ant-state warriors are trained in the prisons. Eventually there is so much frustration in the society that chaos occurs. In many instances, situation has become so bad that people were actually starving before the system broke down. In the advanced technological societies of the Western Democracies, it seems probably that other factors might be important in reaching this tipping point. I'm sure that city freeways at rush hour are one of the most irritating aspects of modern society. A sharp increase in the price of gasoline has the potential to cause social unrest. Re-instituting the draft would be a very dangerous step in the current environment.
A government that provides more services at less cost has more moral authority. As the percentage of the economy controlled by government increases, it gets less and less respect from its citizens. Over time, the emphasis shifts from government social services to the various criminal enterprises the government uses to make its money. The more soldiers, cops, jails, and weapons a government has, and the less useful services it performs, the more likely it is to be overthrown. Thus the governments that seem the most invincible are often the most vulnerable. The US has about a million man in it's armed services. Few of these are actually the kind of fighters that would be useful in a contest with the civilian population, and many of them are overseas. Perhaps there are a couple of hundred thousand that might of some use in an armed uprising, and many of these would no fire on American Civilians. The population of the US is about 290 Million of which at least a hundred million are ready and willing to fight if they become aroused. Many of them have been fiercely misused by the government, having been jailed for trivial infractions, or even infractions they did not commit. If there are a lot of "murderers" who have been proven not guilty because of DNA evidence, there must be many more innocents in jail for lesser crimes where the courts have much less regard for the rights of the accused. There are millions of people who are depressed and full of rage, and quite rationally so. They see their lives as without the possibility of excitement or any real opportunity to advance to a better lifestyle. This may be a widespread illusion, but it is a very dangerous illusion.
In pre-industrial societies, it was easier to predict when governments would fall, and what form that fall would take. In the USA civil war might be more probable than revolution. There are substantial tensions between the eastern and western parts of the Empire. There is residual bitterness in California over the Enron Energy Scam. The 2000 Election remains a point of conflict. There is a major difference in attitudes about the drug war in the eastern and western regions of the country. There are also tensions between rural states dominated by the Republicans and urban states dominated by the Democrats. There is a struggle between organized religion and organized science. There are racial tensions. And there is the age-old struggle between the rich and the poor. As the Chinese say, revolution is what happens when the rich get too rich, and many of the wealthy in the modern world are very wealthy indeed.
There are few obvious signs that the US government or any of its allies are about to fall, but many governments have fallen when few suspected it was about to happen. The most recent example is the surprising dissolution of the Soviet Union.
Of course there is the possibility that the parasitical government could suddenly get good sense and start to have enough concern for its own survival that it will voluntarily stop its growth, but that would be a historical event of the first order, and few knowledgeable observers expect it to happen. Any politician that tries to really limit the growth of government immediately becomes immensely unpopular a lot of powerful special interests. Bill Clinton was a very good example. Perhaps his plan to pay down the national debt had more to do with his unpopularity in certain quarters than oral sex?