A credible one would say convincingly that he will work every day to pare down the federal government, not just in size but in authority, wealth, regulatory activity, military deployment, spending and debt, and in all other aspects. He would promise to do his best to stop government's constant expansion, reverse its growth, start to free Americans from the tax enslavement into which it is driving them, begin to retract the global US economic empire, and get Washington off the aching backs of the American people before they have had enough and throw it off for themselves. He would, effectively, be promising to preserve the United States rather than allow it to crash at the end of the line down which it is now racing.
None is likely to be so honest with us, though. He would believe he would be destroyed by the establishment, from the national political class to its supporting financial sector in what we like to call private industry to its propaganda ministry in the mass media. He will instead lie to us to get elected, all with the best of intentions, and then once in office find he is unable to act in ways contrary to the interests of the establishment because, out of fear of the power arrayed against it, he did not build public support for his cause when he had the chance.
What we will continue to get, then, is presidents who run on status quo platforms, differentiating themselves with marginal issues rather than crucial ones. The runaway federal train will continue careening down the track to its inevitable end. Get ready for the crash. The national state will not accept reform, and so it already is down to every man for himself.