A second guard against tyranny was separation of power which means

A second guard against tyranny was separation of power which means that the Constitution brought about the division of powers between the three branches of Government.

Explanation:

The Constitution of the United States made efforts to guard against vesting powers on only one branch of government (tyranny) by introducing the principles of Federalism, Separation of power, Equality of large and small states, Bill of rights and Checks and Balances. For example, the Legislative branch is responsible for approving the election to the office of the President. They also have the power to impeach the President and remove judges from office.

On the other hand, the Judiciary branch of Government can pronounce on the act of the president as unconstitutional. Without these guards against tyranny, the United States would have been ruled by dictatorship.