I am answering assuming that LEO must mean "Law Enforcement Officer" (the abbreviation is not widely used).
can people in general, and especially politicians or LEOs, be charged
and prosecuted for intentionally violating immigration policies (e.g.
failing to detain someone knowing their illegal status, etc...)?
The short answer is no. But, they can be successfully sued for enforcing immigration laws when they do not have the legal authority to do so, and usually, state and local government officials do not have the legal authority to enforce federal immigration laws. (State and local governments are also generally prohibited from enacting state or local laws pertaining to someone's immigration status.)
In general, the only people with the authority to detain someone for violating immigration laws are immigration officers employed by the federal government. They have absolute discretion in how they enforce federal immigration laws and are free to systematically or on a case by case basis choose not to enforce those laws, as are the executive branch politicians to whom they report.
One of the main reasons that state and local officials cannot enforce immigration laws is that this would interfere with this exclusive jurisdiction of the federal government over immigration and with the absolute discretion of federal officials to decline to enforce the immigration laws or to enforce immigration laws merely on a selective basis.
State and local officials have authority in this regard only if they are expressly authorized to do so by law, and then, only if the state or local government chooses to cooperate by allowing their officials to be used for that purpose.
Generally speaking, the federal government authorizes state and local jail administrators to detain someone pursuant to an immigration hold if the state and local government authorizes the jail to do so. But, usually state and local officials do not have the authority to arrest someone solely for being in the U.S. without having a valid and current immigration status. This authority is largely reserved to Homeland Security officials, although FBI agents in the Justice Department probably also have this authority.
In contrast, generally speaking, someone detained by a state and local law enforcement officer who enforces a federal immigration law, despite not having the legal authority to do so, could prevail in a lawsuit against the state or local law enforcement officer for violating the civil rights of a person detained by someone who had no legal authority to do so. Such suits have prevailed repeatedly in Phoenix, Arizona where a rogue sheriff attempted to enforce federal immigration laws despite not having the legal authority to do so.
Thus, the assumption that the kind of actions involved, for example, in "sanctuary city" policies are intentional violations of immigration law is ill-founded (violating a mere "policy" that is not actually a law is by definition never illegal). Generally speaking, there are no immigration laws violated.
A "coyote" is intentionally violating an immigration law as is someone sneaking over the border when not legally authorized to do so. Someone who doesn't participate in the act of illegal entry, and who does not violate federal employment laws related to immigration (basically requiring an I-9 to be filled out and filed with the federal government), is violating no law.
As a matter of constitutional law, the federal government does not have have the constitutional authority to compel state and local government officials to enforce federal law (although it can authorize and "bribe" state and local governments to do so). Subject to applicable state law, for example, a city government has every right to declare itself a "sanctuary city" and refrain from actively assisting the federal government's enforcement of federal immigration laws.
Also, politicians and state and local prosecutors are absolutely immune from legal liability in connection with performance of their official duties, and law enforcement officers have qualified immunity for their acts.
In particular, law enforcement and prosecutors have essentially absolute discretion to refrain from choosing to enforce any law, and their politician bosses have broad authority to direct how they will exercise this discretion. For example, in general, even if a prosecutor and law enforcement know to an absolute certainty that someone is a serial killer, and can effortlessly arrest that person without any risk of harm to anyone and at minimal expense, they have no enforceable legal duty under U.S. law to try to arrest that person or prosecute that person for any crime. Failing to enforce a known violation of the law is not a crime (unless the failure to enforce is caused by a bribe).
Many millions of people who reside in the United States are deportable but have not committed any crime, so rendering assistance to someone is deportable is not per se assisting someone in the commission of a crime, even after the fact, and indeed, many public officials have a legal duty to aid all "persons" in protecting their legal rights, including people who are deportable.