It seems that a Republican representative interrupting Obama's speech last week with a shouted "You lie!" has pissed a lot of people off and sparked a lot of debate. Some of the debate is about the comment itself, but more of it revolves around the issue of whether a U.S. Representative or Senator should be able to argue with or heckle the president during an important address.
This debate involves issues of politics and public etiquette, but since I really like political history, there is one element of the debate that particularly interests me. I've seen a lot of people point out that in other countries (the United Kingdom/Britain and Canada being the most common examples), the Prime Minister will often face hostile questioning and heckling from their* political opponents, whereas in the U.S. the President almost never has to directly confront their political opponents face-to-face in public.
The basic reason for this is that the US government is set up in such a way that the President of the United States is both the head of state (the official "face" of a national government) and the head of government (the head of the executive branch of government and the single most powerful official in the government). This seems natural to people in the USA, but in quite a few governments, the head of state and head of government are two different people. In constitutional monarchies, like the United Kingdom and the several other nations who recognize the same sovereign, the Queen or King is the head of state, but has no political power. The head of government in constitutional monarchies is an elected official, usually a Prime Minister, who has more actual authority than any other official in the national government. Some nations that have no monarch still have a separate head of state and head of government. Germany, for example, has an elected President who is head of state but who has very limited real power. The head of government, on the other hand, is the chancellor. India has a similar arrangement, with an elected President who has much less real power than the Prime Minister, who is the head of government.
The position of head of state, whether it carries actual power or not, almost always has a special prestige that head of government does not have. The head of state is traditionally a symbol of their entire nation, the "public face" of not just the nation's government, but of the nation as a whole. To directly insult a head of state is often seen as insulting the entire nation.
The system of having a separate head of state and head of government has some advantages over a system like that in the United States where both positions are held by the same person. In a modern democratic society, the head of government is chosen by a specific political party or coalition of parties, and is often obliged to make controversial policy decisions that are certain to provoke intense criticism from their political opponents. In a country where the head of government is not also the head of state, the head of government has no special role as being the symbol or embodiment of the entire nation. The political opponents of the Prime Minister in the United Kingdom or Canada are free to criticize and condemn as much as they want, knowing that none of their criticism can be construed as an attack on the entire nation. The head of state, the person widely seen as the public face of the entire country, does not take any significant part in day-to-day political life, and rarely if ever expresses opinions on politically controversial issues.
In a system like that of the United States, on the other hand, where the head of state and head of government are the same person, the line between the two roles is very blurred. The President is both the symbol and public face of the nation as a whole, and an official elected with the support of a particular political party and allied interests, who is expected to work in support of a particular political agenda that by definition will be supported by some citizens and opposed, sometimes very strongly, by others. When a President's political opponents criticize or outright condemn the President's actions and political agenda as head of government, they may not intend to attack the President's symbolic role as head of state, but because the two roles are held by the same person, any attack or criticism will seem like an attack on both roles to many people. This is closely tied to partisan politics - people who are sympathetic to the President's political agenda or at least neutral are much more likely to see an attack on the President's politics as an attack on the President's role as symbol of the entire nation, while the President's opponents will draw a strong distinction between attacking the President's specific decisions and agenda and the "office of the Presidency", by which they usually mean the President's role as head of state. This applies to both sides of the political spectrum - nothing in U.S. politics is more predictable than that the President's political supporters will generally try to equate strong criticism with an unpatriotic attack on the basic institutions of the United States, while the President's political opponents will emphasize the importance of free and open political criticism, and that the roles will reverse when the Presidency is taken by a candidate from the opposing party.
Obviously, one can object that this is a clear double standard and that any reasonable person should be able to see right through partisan rhetoric and realize that criticism of a President's politics is completely different from a criticism of the United States itself. This is a valid objection, but in my humble opinion it badly overestimates most peoples' ability to completely ignore their own political beliefs. In my experience, what most people consider reasonable political criticism versus an attack on their country's basic institutions depends heavily on their political beliefs. Most people who have any political views whatsoever will tend to give people who share their views much greater leeway when it comes to criticism, while seeing criticism from the other side as being "disrespectful", "angry", "shrill", etc., unless it is expressed in a very mild form. In the case of a President of the United States, this means that most people will interpret anything but the most mild criticism of a President who shares their views as an attack on the President's position as head of state as well as head of government.
*This isn't grammatically correct, of course, but I like to use "they", "them", and"their" as gender-neutral third person pronouns, because in my totally subjective judgment it just looks and sounds better than the clumsy "he or she", "his or hers", etc., and doesn't look as silly as terms like "hir".