A candidate may not be able to, but a nation with the available resources that we do certainly can influence prices, it is gets serious about the matter.
Influence prices, certainly.
But the claim was "Newt equals $2.50 per gallon."
Set prices, no way, unless they are talking about the disaster of price controls.
Crude oil prices are driven by many more things than under the control of the US president. The demand in Asia, wars, spills, other political events worldwide.
I don't believe Newt Gingrich, Michele Bachmann or any of the other major politician make these specific price claims believe than can actual control to that point.
But I do believe, that they believe, that many of the masses are that gullible.