Veto Power and by passing amendments to the constitution .
The framers of the constitution understood that free speech/expression were imperative rights for citizens to have. This is based on their experience as colonists under British control. When ruled by the British, American colonists were forced to pay taxes that they never voted on or approved.
This sparked outrage among some American citizens, causing them to express their concerns in a public manner. This ability to share their views was the cornerstone of America's ability to declare independence from Great Britain. The framers wanted to make sure that once the colonists had their own country that they would have this right to freedom of expression.