As it was he simply cherished his malice and resolved to do Sam all the injury he could in secret.
When Sam organized his expedition at Camp Jackson, Jake had two motives in joining it.

In the first place things around the camp looked too much like genuine preparation for a hard fight with the enemy, and Jake thought that if he should enlist he would be forced to fight, which was precisely what he did not mean to do if he could help it.

By joining Sam's party, however, he would escape the necessity of enlisting, and he thought that the little band was going away from danger instead of going into it.

He thought, too, that if any real danger should come, under Sam's leadership, he could run away from it, or sneak out in some way, and as he would not be a regularly enlisted soldier, no punishment could follow.
This was his first reason for joining.

His second one was still more unworthy.