What was the idea behind manifest destiny?
that all africans are inferior to the americans and thus have no other societal role than to be slaves
that america was the most powerful world nation and had a duty to mediate all world conflicts
that a christian america had the responsibility to teach the rest of the world its religion
that it was right for americans to extend their way of life from the atlantic to the pacific

The idea behind Manifest Destiny was that it was right for Americans to extend their way of life from the Atlantic to the Pacific.

Explanation:

The doctrine of Manifest Destiny is a phrase and idea that expresses the belief that the United States of America is a nation destined to expand from the coasts of the Atlantic to the Pacific. This idea is also used by supporters to justify other territorial acquisitions. The supporters of this ideology believe that the expansion is not only good, but also obvious (manifest) and accurate.  

the debate held in 1980 by carter and reagan was decisive for the elections. while carter tried to convince people that reagan was a "war hawk", reagan put all his efforts in showing the necessity to take care about medicare and the social security advantage. this debate reagan to win the elections