The Antifederalists were particularly concerned about the potential for the president to abuse power, especially in relation to the executive power defined in Article II of the U.S. Constitution. This article grants the president significant authority, including the roles of commander-in-chief of the armed forces, power to make treaties, and the ability to appoint officials.
The Antifederalists feared that these powers, combined with the lack of explicit protections for individual rights, could lead to a strong centralized government that might infringe on the liberties of the people. They argued that without a bill of rights to clearly enumerate and protect individual freedoms, the federal government could overstep its bounds and infringe upon rights such as freedom of speech, religion, and assembly.
As a response to these concerns and to secure ratification of the Constitution, Federalists eventually agreed to add a bill of rights, which became the first ten amendments to the Constitution. This bill was intended to safeguard individual liberties against potential government overreach.