Personally I see “be the change you want in the world” to be the most powerful approach.  But it is much slower. 

for good or ill, it is the person elected President.  More than a CEO of the largest company, who is elected by a handful of faceless board members, politicians are elected by the public to represent us; to lead for us.  And no one moreso than the President, who not only has the awesome powers as the CEO for a massive federal government that exists to serve us, but represents us to the world and is expected to bring us together for a common purpose of betterment.