In 1950, Truman took us into a major war in Korea without Congressional authority. First time that ever happened. He got away with it, too, just as Clinton got away with exceeding the 60-day limit in Kosovo under the War Powers Act. In fact, when Clinton went into Haiti, he had the audacity to proclaim that the Constitution reserved the war-making decision to the executive. It's well known that presidents have gotten accustomed to making law through executive orders, and it's amazing how few of these are ever challenged or stricken down by Congress. The Supreme Court consistently refuses to hear cases concerning power struggles between the other two branches. All you have to do to realize how unequal Congress and the White House are, is to look at how the size and budget of the executive has grown since the 30s, relative to growth in the legislative branch.
The Constitution reserves to Congress the right to declare war, but the War Powers Resolution clearly states that the President can act with something called "specific statutory authorization", whatever that means. It certainly doesn't sound like a declaration of war to me, nor did it to Nixon, who vetoed the whole mess - the implication is that Congress has Constitutional powers far beyond the simple declaration of war granted by the Constitution.
Also, in light of INS v Chadha and subsequent cases, it is not at all clear that the War Powers Resolution could survive a challenge in the courts. Perhaps recognizing that fact, Congress has never chosen to exercise the remedies provided by the Resolution, such as ordering the removal of troops engaged in hostilities, and thereby provoking a court challenge.
Finally, if you want to look at expansion of powers, it is facile to do so without looking at the explosion of federal agencies over the last 70 years, all of which have been created at the behest of Congress, and exist as a result of congressional delegation of authority.
In any case, what this particular article is about is the expansion of federal powers, at the behest of Congress, by legislating virtually everything under the auspices of the Commerce Clause. Such an expansion of federal power has largely come at the expense of state power, not that of the Executive.