All historians understand that they must never, ever talk about the future. Their discipline requires that they deal in facts, and the future doesn't have any yet. A solid theory of history might be able to embrace the future, but all such theories have been discredited. Thus historians do not offer, and are seldom invited, to take part in shaping public policy. They leave that to economists.
But discussions among policy makers always invoke history anyway, usually in simplistic form. "Munich" and "Vietnam," devoid of detail or nuance, stand for certain kinds of failure. "Marshall Plan" and "Man on the Moon" stand for certain kinds of success. Such totemic invocation of history is the opposite of learning from history, and Santayana's warning continues in force, that those who fail to learn from history are condemned to repeat it.
A dangerous thought: What if public policy makers have an obligation to engage historians, and historians have an obligation to try to help?
And instead of just retailing advice, go generic. Historians could set about developing a rigorous sub-discipline called "Applied History."
There is only one significant book on the subject, published in 1988. Thinking In Time: The Uses of Hustory for Decision Makers was written by the late Richard Neustadt and Ernest May, who long taught a course on the subject at Harvard's Kennedy School of Government. (A course called "Reasoning from History" is currently taught there by Alexander Keyssar.)
Done wrong, Applied History could paralyze public decision making and corrupt the practice of history — that's the danger. But done right, Applied History could make decision making and policy far more sophisticated and adaptive, and it could invest the study of history with the level of consequence it deserves.