Dear Democratic/Republican Presidential candidate:
I know that as president, you will care deeply about the long term consequences of your actions and make decisions on that basis rather than for short-term gain. You can prove that to the public, by creating institutions to force your administration and future administrations to think about those consequences of your actions, in the same time period that you make them.
I suggest that you advocate for two new initiatives in the Office of the White House. The first is a White House-sponsored and White House-run Presidential Assessment Conference. This conference will be held in the first year of your term and thereafter once every four years, and it will assess the long term consequences of presidential administrations that ended 25, 50, and 75 years earlier. A report presented to the public and Congress will assess whether the decisions of the three periods worked out best in the long term, and will help the present-day President and public focus on long-term consequences.
The second initiative is to create the Office of Presidential Historian-Advocate. This person will help manage the Assessment Conference, but more importantly, the Historian-Advocate will be the day-to-day reminder for the President and staff members that their administration will eventually be assessed as well. The Historian-Advocate will prepare documents archived for future Conferences that constitute the administration's argument for why it made the best long-term decision based on the information it had available. A Historian-Advocate who witnessesses the most important decisions will be able to do the best possible advocacy, so the president will have an incentive to involve the Historian-Advocate as much as possible.
The functional effect is to have an advocate for the future involved in day-to-day decision making. The President will even have the option of seeking the Historian-Advocate's advice as to which choice will be most easily defended in future Conferences (a young Historian-Advocate might even be present at the future 25 and 50 year Assessments).
Again, I am certain that you have no need for this institutional incentive for long term thinking. Your advocacy of this idea will prove exactly that, because it's an idea that improves the decision-making of presidents that will follow you, in the long term.