Aug. 12. An anonymous whistleblower files a complaint with the inspector general for the intelligence community. The contents of the whistleblower complaint are still secret. Intelligence community Inspector General Michael Atkinson will later determine the complaint to be credible and a matter of “urgent concern,” triggering a legally required disclosure to the House and Senate intelligence committees.

Aug. 15. Coats and Gordon officially leave their positions.

Late August. Lawmakers raise concerns about Ukraine aid being withheld, citing* its importance to defend the former Soviet republic from Russia.

*https://www.politico.com/story/2019/08/28/trump-ukraine-military-aid-russia-1689531

Sept. 1. Zelensky and Vice President Pence meet* as various world leaders are in Poland for a ceremony commemorating World War II. Trump had originally been slated to attend the ceremony but remained in the United States to monitor Hurricane Dorian.

*https://www.president.gov.ua/en/news/volodimir-zelenskij-obgovoriv-z-vice-prezidentom-ssha-vijsko-57065

Sept. 2. Pence says he didn’t discuss Biden with Zelensky, but that he did suggest* that aid was contingent on rooting out corruption.

*https://www.whitehouse.gov/briefings-statements/remarks-vice-president-pence-president-duda-poland-joint-press-conference-warsaw-poland/

“As President Trump had me make clear, we have great concerns about issues of corruption,” Pence said. “The president wants to be assured that those resources are truly making their way to the kind of investments that will contribute to security and stability in Ukraine.”

Early September. Sen. Chris Murphy (D-Conn.) travels to Ukraine and meets with Zelensky. He later tells NBC’s Chuck Todd* that Zelensky had expressed concern about Giuliani’s overtures.

*https://www.nbcnews.com/meet-the-press/meet-press-september-22-2019-n1057416

Sept. 5. The Post editorial board writes* that it had been “reliably told” that Trump was “attempting to force Mr. Zelensky to intervene in the 2020 U.S. presidential election by launching an investigation of the leading Democratic candidate, Joe Biden.”

*https://www.washingtonpost.com/opinions/global-opinions/is-trump-strong-arming-ukraines-new-president-for-political-gain/2019/09/05/4eb239b0-cffa-11e9-8c1c-7c8ee785b855_story.html

Sept. 9. Atkinson notifies the House and Senate intelligence committees that a whistleblower has filed a complaint, but he does not reveal its contents or substance.

Sept. 10. House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) writes* to Maguire demanding Congress receive the complaint.

*https://www.lawfareblog.com/schiff-letters-acting-director-national-intelligence

Trump announces* on Twitter that national security adviser John Bolton has resigned. Trump says it came at his request; Bolton quickly indicates he offered first.

*https://www.washingtonpost.com/politics/trump-fires-bolton-as-national-security-adviser-saying-he-disagreed-strongly-with-many-of-his-suggestions/2019/09/10/13409e2c-d3b9-11e9-9610-fb56c5522e1c_story.html

I offered to resign last night and President Trump said, "Let's talk about it tomorrow."

— John Bolton (@AmbJohnBolton) September 10, 2019
Sept. 11. The Trump administration releases the Ukraine aid it had been withholding.

Sept. 13. Schiff subpoenas* Maguire to compel him to disclose the whistleblower complaint.

*https://www.lawfareblog.com/mysterious-whistleblower-complaint-what-adam-schiff-talking-about

According to Schiff, the DNI’s office, in a letter from counsel, indicates the whistleblower complaint is being withheld because of confidentially and potentially privileged communications by people outside the intelligence community. It is assumed that this refers to Trump.

Sept. 17. Maguire says* he will not testify or hand over the whistleblower complaint. Schiff says Maguire told him he couldn’t “because he is being instructed not to, that this involved a higher authority, someone above.”

*https://www.nytimes.com/2019/09/17/us/politics/dni-whistleblower-complaint.html

Sept. 18. The Post reports* that the complaint involves Trump’s communications with a foreign leader and some kind of “promise” that was made.

*https://www.washingtonpost.com/national-security/trumps-communications-with-foreign-leader-are-part-of-whistleblower-complaint-that-spurred-standoff-between-spy-chief-and-congress-former-officials-say/2019/09/18/df651aa2-da60-11e9-bfb1-849887369476_story.html

Sept. 19. Atkinson briefs Congress in a closed-door session, telling them the complaint involved multiple events and not a single communication. The Post reports the complaint involves Ukraine.

That evening, Giuliani appears* on CNN and denies any wrongdoing by Trump, but also suggests it would be okay if Trump withheld aid in exchange for Ukraine investigating the Bidens.

*https://www.washingtonpost.com/politics/2019/09/20/giuliani-admits-asking-ukraine-about-joe-biden-after-denying-it-seconds-earlier/

“The reality is the president of the United States has every right to say to another leader of a foreign country, ‘You got to straighten up before we give you a lot of money,’ ” Giuliani said. “It is perfectly appropriate for [Trump] to ask a foreign government to investigate this massive crime that was made by a former vice president.”

Sept. 23. Trump suggests* aid to Ukraine may have been withheld over “corruption” issues — without citing the Bidens.

*https://www.washingtonpost.com/politics/2019/09/23/trump-inches-toward-spilling-beans-ukraine/

“If you don’t talk about corruption, why would you give money to a country that you think is corrupt?” Trump said. “So it’s very important that, on occasion, you speak to somebody about corruption.”

Sept. 24. Trump confirms* he withheld the funding but suggests it was because other European countries should pay for Ukraine’s military aid.

*https://www.washingtonpost.com/politics/trump-confirms-he-withheld-military-aid-from-ukraine-says-he-wants-other-countries-to-help-pay/2019/09/24/42bdf66c-ded2-11e9-8dc8-498eabc129a0_story.html

Sept. 25. Trump is scheduled to meet with Zelensky at the United Nations.

Sept. 26. Maguire is slated to testify to the House Intelligence Committee. (He has agreed to do so.)