The statement that best identifies John Adams’ contributions to early American government is:
He was a diplomat and political philosopher who helped Thomas Jefferson write the Declaration of Independence and served as the nation’s first vice president.
However, it's worth noting that while John Adams did play a significant role in the drafting of the Declaration of Independence, he did not directly help Thomas Jefferson write it, as Jefferson was the principal author. Moreover, he served as the second president, not as the first vice president (that was John Adams). So a more accurate description would highlight that he served as the second president and played crucial roles as a diplomat and thinker in the early American government.
If you need further clarification or a specific focus on another aspect, let me know!