How does John Steinbeck portray the power struggle among the men in his novella "Of Mice and Men"?1) how power is presented. 2) what is...

Ironically, in John Steinbeck's "Of Mice and Men," there exists a struggle among the men because of their aloneness.  Set against the dire times of the Great Depression, the men are insecure as they have no real home, they are separated from their families, they have no permanent job and must vie for jobs against strangers; as a result, they become distrustful of one another. In this Darwinian setting, the men have a profound sense of their aloneness. 

The Swiss psychiatrist and influential thinker of the twientieth century, Dr. Carl Jung, contended that the healthy man does not torture others--generally, it is the tortured who turn into torturers. His statement proves true with the personages of  Crooks and Curley.  When the racially isolated Crooks, the stable worker, finds Lennie in the barn, he is hostile and then taunts him cruelly:

'George know what he's about.  Jus'talks, an' you don't understand nothing....This is just a nigger talkin'.....  So it don't mean nothing, see?  You couldn't remember it anyways....S'pose George don't come back no more...What'll you do then?'....

Crooks' face lighted with pleasure in his torture.

At the same time that Crooks tortures Lennie, he also makes the remark that

talkin'...and It don't make no differencece...The thing is, they're talkin, or they're settin' still not talkin'

indicating that the communion of men is what is important.  Thus, he proves the verity of Jung's statement.  Likewise, Curley engages in this power struggle/torture in his isolation as the son of the boss and husband of the temptress-wife.  In his insecurity about being short and insecure about this wife, Curley is pugnacious, wishing to fight anyone in his jealous rages.  He verbally assaults Lennie after he enters the bunkhouse looking for his wife because Lennie smiles as Carlson and Candy insult him.  When Curley punches Lennie, Lennie simply grabs his hand and holds it so tightly that he damages it.

Steinbeck, a socialist, believed in the interdependence of society; this theme is explored throughout the body of his works. And, in "Of Mice and Men," he presents the ill-effects of man's isolation in which the predatory human tendencies of man emerge when there is no friend or family who can help him measure the world and no dreams to give meaning to life.

Slim, with his "God-like eyes," understands,

I seen the guys that go around on the ranches alone.  That ain't no good.  They son't have no fun.  After a long time they get mean.