Final answer:
The U.S. Constitution is amended through Congress with a two-thirds supermajority vote or by a constitutional convention, and while the states may have direct democracy mechanisms, at the federal level, the public cannot propose amendments directly.
Step-by-step explanation:
The U.S. Constitution can be amended either by Congress or by a constitutional convention. The typical way amendments are proposed is via Congress, wherein both the House of Representatives and the Senate must approve a joint resolution by a two-thirds supermajority vote. This resolution is then sent to the states for ratification without requiring the president's signature. Contrary to some state constitutions, where the people can directly propose amendments, in the federal system, the people play no direct role in proposing or amending amendments to the U.S. Constitution.
The founders were cautious about granting powers to the general voting public, hence they included safeties against the direct exercise of popular will, such as the Electoral College system for presidential elections. Furthermore, while the federal level has a more constrained process for amendments, this is in contrast to many state-level processes where direct democracy allows for more public involvement in proposing and passing amendments.