If there is collision between the president and congress, can congress restrain the President in foreign policy making?The president is the foreign...

I agree with both of the above questions, as they have
great specific examples of the power struggle between the two branches.  I wish to add,
however, what is really in my opinion the most effective tool Congress has to restrain
foreign policy: the power of the purse, or the
budget.

While the Constitution designates foreign policy as
an area of the Executive, when we say foreign policy we often mean wars, or foreign aid,
military aid, etc.  In the case of the Iraq or Vietnam Wars, for example, Congress could
end those wars immediately simply by refusing to write any more checks to fund them. 
The President has a very limited amount of discretionary funding to spend as he sees
fit, and certainly not enough to wage a major war, so he depends on Congress to keep
paying the bills, and there is no Constitutional requirement that they continue to do
so.