Who kept check on Jefferson's anti-federalism?

Answer 1

Alexander Hamilton, James Madison and to a lesser extent John Jay. See "The Federalist Papers" for the positions and arguments put forth.

It is also pertinent to learn of the role of George Washington, who came back from Virginia and used his considerable influence to pass the US Constitution. Washington's role in this matter and his refusal to accept a role similar to king are defining moments in US history. In my opinion, making him the most important president in US history.