It is not possible to determine what all three documents agree is the most likely reason people's rights will be threatened without more information about the specific documents you are referring to. Different documents may have different perspectives on what constitutes a threat to people's rights, and what the source of those threats may be.
However, in general, many documents agree that the most likely reason people's rights will be threatened is when government oversteps its boundaries and exceeds its power. This can happen when government officials abuse their authority, when laws or policies are unjust or discriminatory, or when there is a lack of checks and balances to keep government in check.
As for the branch of government that all three documents imply is the source of the people's power, in most democratic societies it is the legislative branch, as it is the branch that makes laws and represents the will of the people. However, again, it is important to know the specific documents you are referring to, to give an accurate answer.