For all intents and purposes, the United States actively teaches its citizens about the genocide on the Natives and settlements have been reached with the descendants of the victims.
But no U.S. Congress and/or President have ever labeled it as a 'genocide'. I've only been able to rely on my deduction skills and I haven't been able to find an official reason for this kind of policy.
What are the historical (and perhaps political or legal) reasons for such a policy?
For all intents and purposes, the United States actively teaches its citizens about the genocide on the Natives
Eh... I don't think so.
I'm from Nebraska and we've got a couple of reservations and a decent sized Native American population. I cannot think of a time where the term genocide was used to describe what happened to the Native Americans. Granted, this is my experience and, assuming high school and older, 20 years ago, but I honestly think you'd be hard pressed to find non-Native Americans in Nebraska who have been taught that what happened was a genocide.
Also, I think your question is too broad. What does genocide mean? What time period are you talking about? What native people are you talking about?
First, what does genocide mean? The Nuremburg Trials charged the Nazis:
They (the defendants) conducted deliberate and systematic genocide—viz., the extermination of racial and national groups—against the civilian populations of certain occupied territories in order to destroy particular races and classes of people, and national, racial or religious groups, particularly Jews, Poles, Gypsies and others.
The UN Convention on the Prevention and Punishment on the Crime of Genocide says:
Any of the following acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such: killing members of the group; causing serious bodily or mental harm to members of the group; deliberately inflicting on the group conditions of life, calculated to bring about its physical destruction in whole or in part; imposing measures intended to prevent births within the group; [and] forcibly transferring children of the group to another group. (Article 2 CPPCG)
There are lots of other definitions, some of which include a much broader scope. I think the UN definition is fairly comprehensive - it includes the phrase "deliberately inflicting on the group conditions of life, calculated to bring about its physical destruction." I like this phrase because it IS broad enough to include things that might not have been considered, yet still brings about the end result - destruction of a people.
What time period are you talking about?
Benjamin Franklin, Thomas Jefferson, George Washington - they were all friendly towards the natives and wanted to live in peace with them. Now, one could argue that a "voluntary" genocide began around then. The Treaty with the Cherokee of 1817 offered 640 acres of land if they became US citizens. Can one be a US citizen and a member of the Cherokee at the same time? Is this the beginning of genocide? I don't believe it is, but others might disagree. Jefferson wrote to William Henry Harrison, the governor of the Indiana territory in 1803:
Our system is to live in perpetual peace with the Indians, to cultivate an affectionate attachment from them, by everything just and liberal which we can do for them within the bounds of reason, and by giving them effectual protection against wrongs from our own people.
He goes on to explain the desire to get the natives to start farming and doing other work and getting them used to a lifestyle similar to Americans so that when the US would expand towards them, they would voluntarily join OR they would move west of the Mississippi. He also mentions that any tribe who wanted to fight should have their lands seized and be forced west of the Mississippi as a warning to the others. Again, on one hand, Jefferson is talking about peace, but he IS talking about changing the native population's culture, but he's NOT doing it to destroy the people. It might be a cultural genocide, but it's not something that is "calculated to bring about its physical destruction."
What native people are you talking about?
If you look at the Hopi and Navajo peoples, the Hopi asked the US government for protection from the Navajo. The Navajo were then marched to a fort where some of their enemies were at and trouble ensued. This shows that 1) the US government was willing to help a native tribe (Hopi) and 2) the US government didn't know enough about the tribes to keep the Navajo and the Mescalero apart.
If we compare this with the southern tribes (Cherokee, Choctaw, Seminole, Creek, Chickasaw), it's night and day. The Choctaw were forced off of their lands in the middle of winter and forced to Oklahoma. En route, they froze to death, they were murdered and robbed by local whites, they starved, and they had no water to drink as the creeks were all frozen. But again, is this genocide? Was this done "to bring about [the native people's] physical destruction in whole or in part"? Or was this just a stupid and/or brutal decision done with little regard for human life?
Looking at the Nuremberg definition, genocide is "deliberate and systematic." I don't think we can say that the US government was deliberate or systematic in wiping out Native Americans.
I think that it's fair to say:
US government policy towards Native American tribes was hostile for at least 50-70 years. (From Andrew Jackson until the mid 1870's (end of the Great Sioux War) or 1890 (Wounded Knee Massacre).
Native American removal policies were harshest against tribes in the East. Tribes out west, having seen what happened, fought back.
US government actions against certain tribes at certain times have been brutal and harsh.
US government actions against certain other tribes can be considered genocide.
/u/Hello_There2 mentioned the Bureau of Indian Affairs apology. It's a good read, and I think it definitely sheds some light on this whole argument.
This agency forbade the speaking of Indian languages, prohibited the conduct of traditional religious activities, outlawed traditional government, and made Indian people ashed of who they were. Worst of all, the Bureau of Indian Affairs committed these against against the children entrusted to its boarding schools, brutalized them emotionally, psychologically, physically, and spiritually.
This is the genocide that is clear. The BIA took native children and taught them to not be Native American. There's more in the speech about the physical destruction - killing bison, alcohol, killing women and children - but in my opinion, the schools is the issue that seems clearly designed to bring about the destruction of the native people. I find it interesting, too, because of all the horrible things that the US DID do, the one that seems the most innocuous (schools) is the one that did the most damage.
So, I would change your question to be more specific.
Why has the US government not apologized for the cultural genocide against the western tribes in the latter half of the 19^th century? (A genocide that an agency of the US government has admitted to)
Was the brutal treatment of Native Americans east of the Mississippi River genocide or simply brutality/stupidity? (Horrible acts that would qualify as genocide if the end goal can be proven.)
So to answer your final part, what are the historical, political, or legal reasons that the President and/or Congress hasn't apologized?
Two things. First, a lack of political clout. Without getting into the 20 year rule, I would not be surprised if a future administration makes an apology in the next 10-20 years. Native American tribes have been getting stronger economically which lends itself to political power. The obvious sign is Indian casinos. The not so obvious is the non-gambling related businesses. The Winnebago of Nebraska have Ho-Chunk corporation, some native tribes in Washington have a fishery they operate - things are getting better for Native American tribes economically. If you look at the history of Columbus Day vs. Native People's Day, I think you'll also find some pretty solid evidence of political changes that have happened/are happening.
Second, a lack of historical awareness and acceptance. People need to be aware of the history (and again, I'm not convinced that they are) so that when a Native chief says, "Hey, we want an apology," people are thinking of genocide and not of the stereotypes of beads for Manhattan or drunk people on a reservation. Then, people need to recognize and accept that what happened was genocide. Until all of those conditions are met, I don't see an apology coming.
All that said, the growing clout of Native tribes, the ability to spread the word these days, a growing awareness - I would not be surprised to hear an apology soon.
On September 8, 2000, the head of the Bureau of Indian Affairs (BIA) formally apologized for the agency's participation in the "ethnic cleansing" of Western tribes. However, you are correct that no President (off the top of my head) has directly labeled the events as genocide or formally recognized the genocide. Genocide remains universally condemned by the international community, but the United States government has been effectively granted de facto immunity from punishment.
By and large, the typical reason for refusing to acknowledge or recognize a genocide is to avoid punishment or the costs of reparations which would need to be paid to the victims of the crimes. In addition, it is quite embarrassing for an administration to admit to faults in its policies, or the policies of past administrations as some might perceive this to make their country/administration "look weak".