For a good part of the United States history Congress contained all the legislative power and war powers. For instance in the two barbary wars, French Quasi war and the war of 1812 where third parties intervention aimed to prevent United States from trading with other willing countries, Congress made a specific demand of military action on the part of the president. Of course the war of 1812 also contained a dark desire on some people's part to take over Canada.
The President's of the time may have started organizing the military before Congress convened but realized that if Congress wanted too it could demand that they return the military back to a non war posture and stationing. Congressional dominance in these areas were a fact and not a mere legality at these times.
Even the land grabbing Mexican American war had Congress be the author of military activity though they were fooled by the Presidents fabrications (they chose to be). Regardless of this blemish the institution of Congress was the prime power when it came to military activity and at least President Polk realized the need to fool Congress to achieve his imperial objective instead of like nowadays where the President simply lets Congress no what he is already doing.
Keep in mind there is no form that a text of declaration of war must contain but it must specify that Congress has made a decision about military activites in a yes or no fashion and cannot delegate that decision to the President such as Congress has done with the Vietnam War, both Iraq wars, and all wars after World War Two. Most of the time the president does not even act as if Congress exists such as with activites in Afghanistan, Grenada, Panama, Kosovo, Bosnia, Haiti, Liberia, Nicaragua, etc.
The start of this modern Presidential war power can be traced back to actions taken by Theodore Roosevelt who took many military actions with out any regard to Congress and these continued escalating to new heights until they hit a wall after woodrow Wilson was defeated from obtaining a third term. During the 1920's these military activities were cut back tremendously by public demand for isolationism from Congress and the elections of three more isolationist presidents.
After the New Deal the Supreme Court that was packed with Franklin Roosevelts supporters (since he won four terms in office!) started to repeal it's earliers precedents that viciously oppossed delegation of legislative authority to the President and the federal agencies he controlled. This why today legislation is always from the executive branch and is almost never from the constitutional method that relied on multiple coalitions.
After this allowance of legislative delegation from career politicans who could now pass the buck the Cold War started. The Cold War lead to the earlier Theodore Roosevelt style of military actions with two thumbs up from the careerist Congress (career politicans increased tremendously after the New Deal), the Supreme Court (loaded with Franklin Roosevelts appointments) and a docile "yes sir" public.
So this presidential elections we yet again wait to elect someone new to hold ALL the power. These reasons stated above are why so many scholars and historians say we live under a new regime they call the 2nd Republic. These scholars and historians seem to think this is a good development.
I forgot to include this Mises review article that talks about this same topic: http://mises.org/misesreview_detail.aspx?control=21
I also forgot that the United States has completely abandoned the constitutional treaty power. You need two thirds of the Senate to ok a treaty which is very hard to do. It is much harder to get two thirds of one legislative chamber than it is to get a simply majority in both legislative chambers.
But the two chamber majority approach is how it is now done. It is called an executive-congressional agreement and it is how the United States is part of the W.T.O and has a myriad amount of military promises with multiple countries governments.
If your worried that the two thirds senate vote for a treaty would harm free trade don't worry. You would just need to cut tariff rates to allow more goods in the country you dont need a treaty to do that. But of course this assumes that politicians actually want free trade.