It’s easy to call an impeachment “historic,” but what kind of history did we really see this week? Most of us couldn’t answer that in real time, but POLITICO Magazine tracked down the tiny handful of Americans who can: the historians and legal analysts who specialize in the rare, high-stakes process of impeachment itself.

This week we invited a group of them to watch the congressional hearings with an eye to what actually made history. They saw quite a bit of it unfold in the hearings on President Donald Trump’s conduct around Ukraine and the conduct of the Congress looking into it.

First, one historian noted the way we consumed the news this week was unprecedented: Unlike during any previous impeachment, we were all able to follow along with the inquiry as it unfolded and witnesses revealed new information. Second, never before, two of the experts pointed out, has an impeachment turned directly on matters of national security. By any normal standard, that should strip the domestic politics out of the proceedings—except, as another historian pointed out, the Republicans in Congress have chosen to act as his legal defense rather than as serious fact-finders about his conduct, which is another historical outlier.

During Friday’s testimony, another piece of history got made: The president, in real time, weighed in with a tweet about the witness while she was being questioned, a move that not only would have been impossible in any previous impeachment process but is very inadvisable because it has the appearance of witness intimidation—as the committee chairman pointed out.

So what will future history books say about the first time a president used Twitter to dig himself deeper into a hole during his own impeachment hearings? We don’t know yet, but it’s clear from historians' answers that we are in the midst of proceedings as singular and disruptive as the president who keeps finding ways to surprise all of us. Every impeachment is a new beast, and as only the fourth impeachment of a U.S. president to hit this point in 230 years, it’s certain we’ll see far more made soon. Here’s what we’ve seen so far: