Over the years presidents have assumed more responsibility for foreign policy. List & at least two problems which may occur if Congress had more control over foreign policy than the President.
Would the war in Iraq have been filibustered? Would the blockade of Cuba ever have made it out of committee? Just as the Constitution specifically gives the federal government power over foreign policy--because to do so at the level of the 50 states would not be practical or possible--so must it be so that the President takes a lead role in foreign policy instead of Congress. Notice how difficult it is to ever get treaty agreements ratified? (Arms control, NAFTA, Kyoto) Other countries would consider a Congressional-directed foreign policy as an American weakness.
Another problem is that you suddenly have 535 different agendas on foreign policy, not just leading to problems in terms of the pace of decisions but also states and constituencies all trying to get what is best for them from from various foreign countries.
Another issue would also be the impossibility of taking responsibility for large decisions since you would always have dissent and chaos when it came time to make decisions whether they require speed or not.
I agree with number 2. There is no way Congress can make a quick and difficult decision. Also, given the huge apparatus that congress is, it is impossible to keep information secret. At any given time, Congress cannot know about all of the information relating to National Security that the president has to know. Therefore the president has to make decisions based on information that is sensitive.
Foreign policy in almost all governments is conducted by one person who has the authority to speak for the government. The sheer act of negotiation itself would be impossible if the 535 members of Congress were necessarily involved. It would be difficult to establish a working relationship with the other side, and the extended process of negotiation would be impossible. The Framers of the Constitution were quite erudite in giving the President the power to make treaties; but only by and with the advise and consent of the Senate.
One would be that there would not be enough focus and promptness in our foreign policy. Congress is not known for making quick and decisive decisions. In foreign policy (especially in emergencies) we can't wait for Congress to debate and debate. Imagine waiting for the Democratic Senate and the Republican House that we have now having to agree on what to do and say about Egypt. It would be slow and chaotic and we really can't have that in foreign policy.