The Federalists were generally favorable towards Pinckney's Treaty, also called the Treaty of San Lorenzo. The treaty, signed in 1795, established 31 degrees north latitude as the southern boundary of the United States and allowed American ships to travel freely on the Mississippi River. In addition, the treaty allowed Americans to store goods at the depot in New Orleans without paying taxes on them. Jay's Treaty with Great Britain, signed the same year, was generally unpopular, particularly among Democratic-Republicans, who felt it gave Britain too much power; however, Pinckney's Treaty was popular among Federalists and Democratic-Republicans alike. Pinckney was a Federalist, and his negotiation of the treaty strengthened the Federalist Party beyond its traditional area of support--the Northeast. Americans felt that the treaty strengthened the U.S. in our relations with European powers.
It should be remembered that the Federalists and Republicans had not yet developed into parties by 1795, when the treaty was signed. Thomas Pinckney himself was aligned with the emerging Federalist faction, so the treaty that bears his name (also known as the Treaty of San Lorenzo) was popular among Federalists, and in fact increased their popularity outside of the Northern states from which they drew most of their support. The main concession made by Spain in the treaty, the right to free navigation of the Mississippi, was a boon to settlers who were beginning to pour across the Appalachians into the West. They needed access to the river, and to New Orleans, to transport their crops to market. A previous treaty with Spain, the Jay-Gardoqui Treaty, had failed to guarantee this right. While the West would fall solidly in the Jeffersonian Republican camp over the next decade or so, Pinckney's Treaty was a large step toward securing the loyalties of Western settlers to the United States, and this was hardly a given in the late eighteenth century. It also secured the borders of the United States with Spain. For all these reasons, Pinckney's Treaty was popular with Federalist-leaning politicians as well as with most Americans.