July 3: A hold is placed on the aid to Ukraine.
July 10: Ambassador Sondland announces during White House meeting that Ukrainian President Zelensky would get an Oval Office meeting with Trump if they agree to launch investigations.
July 19: Sondland emails Sec of State Pompeo, and Chief of Staff Mulvaney that he spoke with Zelensky who said he is prepared to run an investigation
July 25: In text message between Andriy Yermak, a high ranking Zelensky aid, and NATO Ambassador Voker. Volker tells Yermak that Zelesnky will get a White House meeting if Zelensky convinces Trump that he will investigate.
July 25: Ukrainians contact the DoD to ask about aid being withheld
July 25: Trump has phone call with Zelensky. Trump asks Zelensky to investigate the Bidens, and CrowdStrike(who determined that Russia broke into the DNC network and stole emails). Zelensky says that he will investigate and that an aid to him spoke to Giulliani.
Aug (Early): Sondland speaks with Trumps personal lawyer Giulliani for the first time. "Giuliani emphasized that the president wanted a public statement from President Zelensky committing Ukraine to look into corruption issues. Mr. Giuliani specifically mentioned the 2016 election (including the DNC server) and Burisma as two topics of importance to the president.” -Sondland
Aug 10: In a text message between Yermak and Voker. Yermak states that they intend to hold a press briefing during which they will announce a White House visit and investigations into Burisma and election meddling.
Aug 12: The whistleblower files a formal complaint to Congress.
Aug 28: Politico publishes that military aid is being withheld to Ukraine.
Sept 1: “I mentioned to Vice President Pence before the meetings with the Ukrainians that I had concerns that the delay in [US military aid to Ukraine] had become tied to the issue of investigations, I recall mentioning that before the Zelensky meeting.” - Sondland
Sept 9: Three house committees announce investigations into why the aid was being withheld.
Sept 9: Trump and Ambassador Sondland have a phone call on an unsecured line with Sondland calling from a public restaurant. During which Trump conveys to Sonland that he wants no quid pro quo.
Sept 11: Aid was released.