WASHINGTON — The report on the investigation by the special counsel, Robert S. Mueller III, will be made public on Thursday, and unless you’re a counterintelligence analyst, you may have lost track of how we got to this point in the saga and what Mr. Mueller was investigating in the first place. Here is a guide to what has happened over the past three years (yes, it’s been that long) and what we learned.

March 2016

Russia attacks the American presidential campaign.

Military intelligence officers in Moscow, working for the agency known as the G.R.U., used phishing emails and malware to hack into the Democratic National Committee and the Gmail account of John Podesta, Hillary Clinton’s campaign manager.

Meanwhile, operatives at the Internet Research Agency, a private company in St. Petersburg with Kremlin ties, accelerated their influence campaign, posing as Americans on Facebook and Twitter to mock Mrs. Clinton, promote Mr. Trump and sow discord. Other operatives came to the United States to gather intelligence and coordinate with unwitting Trump campaign staff to organize rallies, according to an indictment.

They were all aspects of a broader Russian operation that began in 2014, court papers show. American intelligence agencies would conclude that President Vladimir V. Putin of Russia ordered the intervention. Though it began well before Mr. Trump announced his run, Mr. Putin, who had long despised Mrs. Clinton, was later drawn to Mr. Trump’s Russia-friendly stances. As Mr. Trump gained ground in the race, the Russian operatives adjusted their targets accordingly.