what is purpose of the two metaphors kennedy uses in the phrase if a beachhead of cooperation may push back the jungle of suspicion

Kennedy uses the metaphors to conclude his argument that the U.S. and its adversaries must cooperate and reject their suspicions of each other.

Explanation:

"valley of salt tears" and "dark, deep and foggy" are two images used to establish a mood of uncertainty and regret. this imagery is made up of sensory appeals to brings up   theological concerns of sin and retribution.

they conjure up the human   uncertainty about the divine and its relationship to the world.