These candidates of course know that they cannot address these issues on their own. They know that only Congress can actually pass laws. The candidates also know that a role of the president is to set the agenda for Congress and to show leadership in trying to get Congress to pass the laws that they (presidents) think are needed.
A major role of the president is to lead the country in the direction he (no women yet) wants it to go. Presidents and candidates know they can't do this by simply issuing laws on their own. They know that they have to suggest laws and try to persuade Congress and the public to support those laws.
Only the president can really do this effectively. Most Americans do not know any of the leaders of Congress. They would not pay much attention to the Congressional leaders speeches and such. But when the president speaks, it is big news. Because of that, the president is much more able to lead the country because he has what Theodore Roosevelt called the "bully pulpit."
So, these candidates know they can't rule by decree. But they know that it is the president's job to try to lead the country and the Congress in the right direction.