Dunmore thinks that the Americans will totally go anti British and would revolt against them.
Explanation:
John Murray who was the fourth earl of Dunmore was popularly known as Lord Dunmore. He was a colonial governor in the American colonies which were under the authority of the Britishers.
He was famous for the proclamation which said that the slaves who would be fighting for the British army will get freedom and will be set free by the Britishers. Thus this made the people go anti British.