What happened Monday

Fiona Hill , the president’s former top adviser on Russia and Europe, testified privately before House investigators. She was expected to say that she and other Trump officials strongly objected to the removal of Marie Yovanovitch as the ambassador to Ukraine.

Ms. Hill viewed that dismissal as an egregious abuse of the system by allies of President Trump who were seeking to push aside a perceived obstacle to their own foreign policy goals, according to a person familiar with her account.

Ms. Hill, who left her job on the National Security Council just days before the July 25 phone call between Mr. Trump and Ukraine’s president, was the first person who worked in the White House to be interviewed by House investigators.

Why can’t we see the witnesses testify?

Ms. Hill, like other witnesses in the impeachment investigation, testified privately — meaning it will take time to see a verbatim version of what she told investigators, if we see it at all. My colleague Nick Fandos, who was on Capitol Hill today, explained to me why Democrats are doing so much out of public view:

The Democrats are trying to collect as much information as possible as quickly as possible. Big made-for-TV hearings are a chaotic and clunky way to try to build a body of evidence. They allow witnesses to line up their stories in advance and could easily backfire on Democrats trying to build a public narrative in real time. Most congressional veterans would tell you that from a fact-finding point of view, you are better off following the Watergate model: Investigate in private first, then choreograph a series of public hearings that recreate for the public what the investigation found. Republicans, nevertheless, are accusing Democrats of impeaching a president in secret.

What do the witnesses this week have to tell us?

Democrats believe that two witnesses — Ms. Hill and Gordon Sondland, the Trump donor-turned-ambassador who inserted himself into Ukraine policy — are critical to understanding the July 25 call Mr. Trump had with Ukraine’s president, Volodymyr Zelensky. I talked to Julian Barnes, who covers national security and the C.I.A., about the larger story.

Julian, what did Ms. Hill’s testimony tell us about the impeachment investigation?

What Ms. Hill likely helped outline today was the difference between our official foreign policy and the real foreign policy. Fiona Hill is the National Security Council official who, until her departure this summer, was supposed to be in charge of Ukraine policy and advise the president on it. But what we will likely learn from her appearance is that she was largely cut out of it. There’s this other foreign policy going on, directed by other people like Gordon Sondland, who were working on parts of this Ukraine policy that she never knew about.

Why is it important that Ms. Hill wasn’t the one handling Ukraine policy?

Mr. Sondland is the American ambassador to the European Union. On the books, he should have nothing to do with Ukraine. Ukraine is not part of the E.U. But in reality, he was tasked by Mr. Trump to work on Ukraine policy. He was deep in the mix of forming Ukraine policy, pushing the Ukrainians on what Mr. Trump was after.

So if Ms. Hill and Mr. Sondland were working on the same project — Ukraine policy — from competing lanes, how might that affect their testimony?