One of the pros for the nuclear deal is that as Americans we wouldn't have to worry about a nuclear weapon being made for roughly about 10 years. Keeping Iran at a 5% uranium level would help us eliminate any threat to the United States until we find a better solution.

Yes ,while this is true congress can pass a law that contradicts the executive order to make it ineffective or in other words useless.

The legislative branch is more powerful than the executive because according to the constitution in Article I section 8 it states "To make all laws which shall be necessary and proper... all other Powers vested by this constitution in the Government of the United States" This proves that congress can make any law that they please or need just by classifying it with the Elastic clause. It has to pass by the president but if he veto's it then congress can override the presidents veto and bring back the law. The law will be passed of course with 2/3 majority vote in both chambers.

The legislative branch is much more powerful than the executive branch because congress has to approve the presidents treaties. The president can make the treaty but if it does not pass the House and the Senate with 2/3 majority vote then the treaty is no more. As stated by the treaty clause "The president … shall have the power,by and with the advice and consent of the senate,to make treaties..." Congress has rejected 21 treaties and passed several more but most of them were later withdrawn.