Giuliani's journey to the center of Trump's impeachment battle started with a phone call in 2018
By Michael Warren
How a Shadow Foreign Policy in Ukraine Prompted an Impeachment Inquiry (Published 2019)
By Andrew E. Kramer, Kenneth P. Vogel & David E. Sanger
Trump impeachment inquiry poll: CBS News poll finds majority of Americans and Democrats approve of impeachment inquiry against Trump
By Fred Backus, Anthony Salvanto & Kabir Khanna