Congress' primary power, in terms of U.S. government, is the power of money. Congress gets their way over other branches of government because they are the sole governmental body that can assign budgets and approve spending -- at least when it comes to federal projects.
For instance, when Montana wanted to keep its speed limit at 80+ mph, Congress (through the executive branch's road department, the Department of Transportation) said, "If you don't do it our way, we will withhold federal funding for your highway projects." Even though Congress cannot withhold too much (MAX of 5 percent, I believe, without triggering some kind of review), that money is usually so vital to states that they comply. Some don't, of course, as that was the controversy over the drinking age.
So I wonder, does the Senate here have the power to withhold funds?