After graduating from Yale, Crocker taught mathematics for a short time at the Ellington School before he was licensed to preach by the Hartford South Association of Ministers.
The following year, he published a 300-page historical account of the schism, The Catastrophe of the Presbyterian Church, in which Crocker discussed the controversies had led to excision of the synods.
The plan, largely designed to facilitate western expansion and evangelism in both the Congregational and Presbyterian churches, had prompted much controversy over a number of social, political, confessional, and theological matters.
Crocker's account, in many ways a defense of New England and New Haven position, also argues for the effectiveness of the plan for "Those that were organized under it, from the Hudson to the Mississippi, (who) appreciated its blessings."
Elucidating upon this final reason, Crocker notes ten specifications that ultimately demonstrate why the Plan of Union, according to the General Assembly of 1837, "has had the slow but inevitable effect to subvert the order and discipline of the Presbyterian Church."