Explanation with the answer:
Normalcy means when someone is a state of being normal, usual, or expected.
While Harding was serving in the Senate, the republican party nominated him as their presidential candidate for the election of 1920. Harding's campaign promised a return to "normalcy," rejecting the activism of Theodore Roosevelt and the idealism of Woodrow Wilson.
So they used the word normalcy to mean their campaign will and was promised to return back to normal.
