The main strength of the legislative branch is that it has almost all of the legislative power in our country. That is, it is the branch that actually has the power to make laws. Of course, it is true that the president can veto laws that Congress passes. However, Congress can override his veto if it wishes. More importantly, the president cannot actually make any laws. When President Obama wanted to create the health insurance system that we now call “Obamacare,” he had to ask Congress to pass the law. He was not able to make it happen simply by saying he wanted it. Because only Congress can make laws, it is a very strong branch of government.
The major weakness of Congress is that it is so big. There are 535 voting members of Congress. Even the Senate, which is much smaller than the House of Representatives, has 100 members. This means that no individual member of Congress is very well-known to the general public. Because no members of Congress are really well-known, they cannot easily lead. If a member of Congress wants to propose a major change in policy, he or she will have a very hard time getting most Americans (or even other members of Congress) to pay attention. A member of Congress who tried to propose something really big (like Obamacare) would have a hard time persuading the public to support the proposal because no one would pay attention to them.
Congress is strong, then, because it has the power to make law. However, no individual member of Congress can typically exert much leadership on the national stage. Therefore, Congress is at least somewhat weak because it cannot usually lead the country.