United States Capitol, the building where the Congress meets
First, a few words about the legislative (or "law-making") branch: The Constitution says that "All legislative powers herein granted shall be vested in a Congress of the United States, which shall consist of a Senate and House of Representatives." (Source: Article 1, Section 1) This is one of the most important "balances" in the Constitution; because like the British Parliament it was modeled on, the legislative body of the United States is divided into two separate houses - analogous to the "House of Lords" and the "House of Commons" in British parliamentary government. This "bicameral" (or two-house) legislature is a big part of the reason why the Congress's power is as limited as it is, because it is sufficiently divided among multiple members to make it hard for any one "special interest" to gain control of it. (More on how each one is elected here, and how representation is determined here; if you seek further information on the subject.)
Parliament of Great Britain, the model for the U. S. Congress
In an attempt to reduce confusion about how much power is granted to the Congress, the Constitution actually listed explicitly some of the powers thus granted (Source: Article 1, Section 8, which has 18 clauses in it), and listed a few others that were forbidden just as explicitly - such as how "No bill of attainder or ex post facto law shall be passed" (Source: Article 1, Section 9, Paragraph 3). (If you don't know what these kinds of laws are, don't worry - I will go into them elsewhere in my post about the courts, which discusses why they are prohibited by the Constitution.) Of the powers that are granted, two of them are so important that I cannot leave them out of this post: the power to tax, and the power to declare war - a check upon the power of the executive to wage war without popular support, because it requires the president to get the financing for any such wars through Congress (and Congress alone), and to have its declaration that it is legal for him (or her) to be out there waging these wars in the first place.
Headquarters of the United States Department of the Treasury (which administers the IRS)
Even in peacetime, however, the power to tax is one of the most important powers of the Congress; since the executive branch is totally dependent upon the legislature for all funding, and often cannot operate without it. This was actually one of the most important improvements that the Constitution made over its most immediate predecessor, since the "Articles of Confederation" did not have any compulsory taxing power at all, and thus had a government that was perpetually devoid of revenue - perhaps the most important single reason for adopting the Constitution to begin with. The Constitution's explicit list of powers ended with one of the most controversial parts in its own time, though, which was the clause known to us as the "necessary and proper" clause. This clause said that the Congress shall have power "To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or officer thereof. (Source: Article 1, Section 8, Paragraph 18) The vagueness about what is "necessary and proper" - and specifically, over who would have the important power to decide what is "necessary and proper" - was seen by the people of this time as a major weakness in the Constitution, and created a certain amount of mistrust in a number of the Constitution's opponents.
Headquarters of the Internal Revenue Service (or "IRS"), the tax collecting agency of the United States
In the Federalist Papers, Alexander Hamilton responded to this charge by saying that "a power to lay and collect taxes must be a power to pass all laws necessary and proper for the execution of that power; and what does the unfortunate and calumniated provision in question do more than declare the same truth, to wit, that the national legislature, to whom the power of laying and collecting taxes had been previously given, might, in the execution of that power, pass all laws necessary and proper to carry it into effect?" (Source: Federalist No. 33) He then observed that "I have applied these observations thus particularly to the power of taxation, because it is the immediate subject under consideration, and because it is the most important of the authorities proposed to be conferred upon the Union. But the same process will lead to the same result, in relation to all other powers declared in the Constitution. And it is expressly to execute these powers that the sweeping clause, as it has been affectedly called, authorizes the national legislature to pass all necessary and proper laws. If there is any thing exceptionable, it must be sought for in the specific powers upon which the general declaration is predicated. The declaration itself, though it may be chargeable with tautology or redundancy, is at least perfectly harmless." (Source: Federalist No. 33) In other words, Hamilton argued, if Congress doesn't have those powers "necessary and proper" to carry its power of taxation into effect (or any other power, for that matter), then it doesn't really have this power of taxation (or any of these other powers) at all - something which would be injurious to the Union, when a government needs steady revenue to operate. Thus, Hamilton concluded, the "necessary and proper" clause is not the "threat to liberty" that its opponents made it out to be, but is at the most merely redundant.
Capitol Dome, on the building of the United States Congress
As this clause makes clear, the Congress has a great deal of power given it by the Constitution; but the very parts of the Constitution detailing the process by which it may make these important laws also specify one of the major "checks" (or restraints) upon this power, which is the presidential "veto." The word "veto" is never used in the Constitution itself, but the process is described explicitly in some of the most important passages of the Constitution, and allows the executive branch (specifically, the president) some important power to "check" the excesses of the legislature. Here are the relevant portions:
"Every bill which shall have passed the House of Representatives and the Senate, shall, before it become a law, be presented to the president of the United States; if he approve, he shall sign it, but if not, he shall return it, with his objections, to that house in which it shall have originated, who shall enter the objections at large on their journal, and proceed to reconsider it. If after such reconsideration, two thirds of that house shall agree to pass the bill, it shall be sent, together with the objections, to the other house, by which it shall likewise be reconsidered, and if approved by two-thirds of that house, it shall become a law." (Source: Article 1, Section 7, Paragraph 2)
Capitol Dome at night
The paragraph continues:
"If any bill shall not be returned by the president within ten days (Sundays excepted) after it shall have been presented to him, the same shall be a law, in like manner as if he had signed it, unless the Congress by their adjournment prevent its return, in which case it shall not be a law." (Source: Article 1, Section 7, Paragraph 2)
"Every order, resolution, or vote to which the concurrence of the Senate and House of Representatives may be necessary (except on a question of adjournment) shall be presented to the president of the United States; and before the same shall take effect, shall be approved by him, or, being disapproved by him, shall be re-passed by two-thirds of the Senate and House of Representatives, according to the rules and limitations prescribed in the case of a bill." (Source: Article 1, Section 7, Paragraph 3)
Thus the Constitution has some important checks on the law-making power of the Congress.
If you liked this post, you might also like:
How each house of Congress is elected
How representation in Congress is determined
The executive branch: A single president subject to impeachment and removal
The judicial branch: The power of the courts (and its limits)
The Constitution: The "supreme law of the land" (which is difficult to amend)
Part of a series about
The Constitution itself, and the story behind it
Convention at Philadelphia: The writing of the Constitution (1787)
Preamble: The Constitution's mission statement, with some thoughts about separation of powers
The Congress: Its power to make laws, and the president's power to veto them (in some cases)
Frequency of elections: So how long do all of these people serve, anyway?
Representation: So who decides how many votes each state gets?
Slavery: The complicated legacy of the "Three-Fifths Clause"
The presidency: Powers of the executive, and their being subject to impeachment
The courts: "Good behaviour," some important judicial powers, and how they're appointed
Miscellaneous: Amendment process, "supreme law of the land," and some closing remarks
Debates over the Constitution, then and since
Debates over ratification: Whether to adopt the Constitution in the first place
The "Federalist Papers": Frequently asked questions about them, and why they're important
Debates over checks & balances: Do they actually conflict with separation of powers?
The Bill of Rights: Important in the debates over ratification (adopted 1791)
The Constitution today: Some thoughts about civics education