Final answer:
President Wilson was within his Constitutional powers to negotiate a treaty after WWI, as granted by Article II, Section 2 of the Constitution.
Step-by-step explanation:
Yes, President Woodrow Wilson was within his Constitutional powers when he negotiated a treaty after World War I. This power is addressed in Article II, Section 2 of the U.S. Constitution, which grants the president the authority to make treaties, provided two thirds of the Senate concur. The Treaty of Versailles officially ended World War I, and Wilson played a significant role in shaping its terms, including advocating for his famous Fourteen Points and the establishment of the League of Nations.