Complex sentence: Secondly, in appointing George B. Cortelyou as his campaign manager, Roosevelt had purposely used Parker's former secretary of commerce because Cortelyou, knowing the secrets of the corporations, could extract large contributions from them.
Split into simpler sentences: Secondly, in appointing George B. Cortelyou as his campaign manager, Roosevelt had purposely used Parker's former secretary of commerce. This was of importance because Cortelyou, knowing the secrets of the corporations, could extract large contributions from them.