To quote a current sitting US Supreme Court Justice: "Nothing prevents Congress from passing a stupid law."
Laws are either Constitutional (i.e. they adhere to the restrictions put forth in the US Constitution), or they are not. The ultimate decider of this question is the US Supreme Court. But that is the SOLE criteria for laws.
Thus, it is entirely possible for Congress to pass (and the President sign ) a law which is stupid, crass, unfair, or unjust, so long as the Supreme Court agrees that the law does not violate any Constitutional principle. Now, the vast majority of laws which the average person would consider "unjust" would fall afoul of the Constitutional principles of Equal Protection under the Law or Due Process.
In general, the President (and through him, the Department of Justice) is obligated to enforce laws that have been passed. That is, the President's change to declare the (proposed) law unjust and unenforceable came BEFORE it was signed into law by him. Afterwards, as the properly passed law, the President is obligated to enforce it.
There are two exceptions to this obligation, one which is reasonable, one which is dangerous.
The first is when the Constitutionality of the law is up for challenge - that is, when there is an active court case moving through the Federal judiciary regarding the law in question. Sometimes a Federal judge will declare that the law is to be suspended until the case has been completely resolve (a preliminary injunction against enforcement). Here, the President CANNOT enforce the law, as it is suspended until the case is resolved. In other cases, the President may decide that the court case has a good chance of prevailing and overturning the law, and that the prudent thing to do is to have the DoJ suspend enforcement until the case is finished. This situation is totally at the discretion of the President.
The second case where a President may decline to enforce a law is through what is called a "Signing Statement" - this is a declaration that the President makes during the signing of a bill (passed by both houses of Congress) into law, where the President makes statements about how he will direct the DoJ to enforce (or not enforce) the law. Legally speaking, this is exceedingly grey, and, in the opinion of many Constitutional scholars, unConstitutional, as the President is not supposed to be unilaterally deciding which laws to enforce or how to interpret the laws.
Back to the original question: if the law in question has been declared legal by the courts, the President MUST enforce it, whether it is just or not. Citizens have the option to protest and stage civil disobedience, but the President does not - he is NOT empowered to make determinations of legality of laws.
Remember there is a distinction between "unjust" and "unConstitutional". If a law has been declared Constitutional (either by an explicit ruling of the Judicial branch, or, by a lack of any legal challenge to it's Constitutionality), then the President is legally obligated to enforce that law. A legal law does not have to be "just". Because "just" is a social concept, not a legal one.
And, of course, remember that Congress originally passed that law, so if someone considers it unjust, then it's really Congress' fault, not the President. The President is NOT responsible (in the legal sense) of being At Fault for enforcing any law.
Of course, the ultimate answer is that Congress should pass a new law replacing the old one.
The President isn't King - he (or she) does not get to decide which laws to enforce and which to ignore. He must enforce ALL legal (Constitutional) laws, and complaining that laws you don't like are being enforced by the President isn't the President's fault.
If a law is passed that is unjust or against the constitution it will end up in the Supreme Court. The president doesn't enforce it. He doesn't have that kind of power.
The jaw has to be just so this question shouldn't even be asked.
The executive branch enforces the law, while the judicial branch interprets the law. Congress only makes the laws.
The Legislative branch (congress) makes the laws - but the president of the US can either approve of the law, which enforces the law into action, or it can veto the law, which Congress can then override the veto with a 2/3 majority vote.The straight answer would just be Congress. The indirect answer would be Congress and the Executive branch (president).
The executive branch, which includes the president, state governors, military, and police, enforces the law.
Whenever a U. S. President is in violation of the law as interpreted by the U. S. Supreme Court (or even if he/she is in violation of a law that the Supreme Court has not tested), it is the responsibility of Congress to impeach him/her.
the congressThe legislature branch enforces them so the judiciary branch must make them. After that the law is passed to Congress where they and the president must pass or decline the bill. If it is passed and approved it becomes a law.
Can the President ask the congress to make a law?
The president enforces the law, vetoes laws, and makes treaties.
the congress can veto a law the president passed
The executive branch.
Judicial- The judicial branch of government approves laws. It determines whether it is constitutional to have such a law. Supreme Court. Legislative- Writes the laws. Has the power to declare war. Congress Executive- Enforces the law. President and his Cabinet.
What the congress has to do first is they have to get a hole lot of people to say YES to the law. They have to out vote the president.
No branch of government has ultimate control. Thankfully we have something called separation of powers (checks and balances). Example Congress legislative branch make laws. the president executive branch enforces them. the courts the judicial branch decides whether the law are constitutional. They interpret the law. Sadly over the years congress and given powers and extended the powers to the president.