The Democrat-led House of Representatives is leading an impeachment inquiry into President Trump. While momentum toward impeachment had been building among Democrats for months, House Speaker Nancy Pelosi, D-Calif., announced a formal inquiry in September — after a whistleblower complaint about a White House phone call with Ukraine.

In a call with Ukrainian President Volodymyr Zelenskiy, Trump asked for an investigation into a debunked conspiracy theory about the 2016 election and into potential 2020 rival and former Vice President Joe Biden. The White House is also accused of withholding military aid to Ukraine for Trump's personal political gain. Trump maintains that he has done nothing wrong.

Here is the key information you need in order to understand an increasingly complicated affair. Read the latest coverage of the inquiry here.

---

Timeline: The Ukraine Affair

Here's how we got to the impeachment inquiry, from Trump's early focus on Ukraine in 2017, to the release of the whistleblower complaint on Sept. 26. Read the timeline.

---

Who And What: Key People And Concepts

Since the original whistleblower complaint was released, the list of names of those connected to Trump's call with Zelenskiy or to broader Ukraine policy has grown substantially.

From the president to career diplomats to private lawyers, here is a quick guide to people connected to the events being investigated.

In-depth profiles:

• Lev Parnas and Igor Fruman: A complicated web connects two Soviet-born businessmen with the inquiry
• Rick Perry: How the energy secretary became a key figure
• Adam Schiff: The surprising face of the impeachment inquiry
• Gordon Sondland: The ambassador whose texts put him at the center of the Ukraine scandal
• Marie Yovanovitch: How the former ambassador became a target in Ukraine

---

Documents: Primary Sources

Written words are central to the Ukraine affair. The significance of the whistleblower's original complaint and the White House's record of its call with Ukraine are debated, but the text is public. Here are the documents to refer to as the inquiry proceeds:

• The White House memorandum of the call (Sept. 25)
• The Pentagon letter on military aid to Ukraine (Sept. 25)
• The whistleblower complaint (Sept. 26)
• Batch of texts between diplomats released by House Democrats (Oct. 4)
• Gordon Sondland's written testimony (U.S. ambassador to the European Union, Oct. 17)
• William Taylor written testimony highlights (acting U.S. ambassador to Ukraine, Oct. 22)

---

Tracker: House Members Who Back Impeachment

Even before the House speaker announced a formal inquiry, Democrats were calling for impeachment proceedings. Here is where they stand ahead of a potential vote on articles of impeachment.

More: Who In The House Is Calling For Impeachment?

• 
•