No.
Congress can REPEAL any law, constitutional or not. Only the Court can overturn a law because it is unconstitutional.
"Don't Ask, Don't Tell" is a federal law, which Congress would have to repeal, unless the Supreme Court finds the law unconstitutional.
It can not as it is the law of the land and upheld by the Supreme Court. Another view. Yes, they should repeal it, as it is a trainwreck. Much more expensive than we were led to believe, and difficult to implement. Congress has the authority to repeal any law.
In the US, when congress eliminates a law this is called a repeal. When the Supreme Court finds a law unconstitutional, this is called "striking down" a law.
Supreme Court interprets the law according to the constitution so they can stop, repeal, or support a law.
The common citizens elect the Congress members, who write the laws. If the people dislike a law that Congress passes, they can elect new members to repeal the unliked law.
The President does not have the power to "repeal" any laws on his own. The only way a law can be repealed is through the same process that any law is made: a bill repealing the law would have to be passed by both houses of Congress and then signed by the President.
All legislative power is vasted in Congress, including the right to repeal or amend its Acts. States have similar legislatures which can enact law and amend them, as long as they adhere to the law of the Federal government.
Yes. In order to repeal a law, Congress must introduce new legislation which states that a previous law (Health Care Reform, Don't Ask Don't Tell) is repealed. Theoretically, if the Senate did pass a bill which repealed the Health Care Reform Act, then it's up to President Obama to veto the bill. This would place the veto subject to an override by a 2/3 super majority in each chamber of Congress. Currently, the House does not have to votes to over ride a Presidential veto.
Repeal
No, not alone. Only congress can repeal the law or write new one. The president can recommend to congress what he wants. The president also can veto the law written by congress or agree and sign it. But it should be noted that President Obama wants to keep some of the Bush tax cuts-- for the middle class especially. But he feels the wealthy do not need another tax cut, when they have already gotten a number of them.
A Congress can repeal legislation like the Affordable Care Act (ACA) by passing a new law that explicitly nullifies the existing law, which requires a majority vote in both the House of Representatives and the Senate. The President can then sign this legislation into law. Alternatively, Congress can use budget reconciliation to expedite the repeal process, allowing certain provisions to be repealed with a simple majority in the Senate. Additionally, the Supreme Court may also invalidate laws if they are deemed unconstitutional, but this is a judicial rather than legislative process.