Congress is not deposing European Union Ambassador Gordon Sondland on Tuesday as planned, after an 11th hour intervention from the Trump administration to block his testimony.

So with questions concerning him still unanswered, we thought it would be a good time to step back and look at the major unknowns in the Ukraine situation.

Here are four of them.

1. What did Sondland tell Sen. Ron Johnson?

There’s one quote Republicans cite as their best evidence that there was no quid pro quo between Trump and Ukraine. It came in this exchange between Sondland and the U.S. chargé d’affaires in Ukraine, Bill Taylor:

TAYLOR: As I said on the phone, I think it’s crazy to withhold security assistance for help with a political campaign.
SONDLAND: Bill, I believe you are incorrect about President Trump’s intentions. The President has been crystal clear no quid pro quo’s of any kind. The President is trying to evaluate whether Ukraine is truly going to adopt the transparency and reforms that President Zelensky promised during his campaign I suggest we stop the back and forth by text If you still have concerns I recommend you give Lisa Kenna or S a call to discuss them directly. Thanks.”

President Trump tweeted the quote Tuesday morning.

But as was quickly noted when the texts were released, Sondland’s verbiage sounds a whole lot like a man who knows these texts might one day see the light of day and is trying to toe the company line. It’s also notable that he then tries to take the conversation offline (where there would be no paper trail). And Sondland, unlike the career diplomats he was conversing with, was a major Trump donor.

But even if you take this at face value, that was Sept. 9. And we recently found out that, as of late August, Sondland was apparently singing quite a different tune. That’s according to what Sen. Ron Johnson (R-Wis.) told the Wall Street Journal on Friday:

Under the arrangement, Mr. Johnson said Mr. Sondland told him, Ukraine would appoint a strong prosecutor general and move to “get to the bottom of what happened in 2016 — if President Trump has that confidence, then he’ll release the military spending,” recounted Mr. Johnson.
“At that suggestion, I winced,” Mr. Johnson said. “My reaction was: Oh, God. I don’t want to see those two things combined.”

Johnson tried to clean this up a bit this weekend, but he didn’t really shed much light. He emphasized that he confronted Trump about the possibility, and Trump denied it. But of course Trump would deny it, and that doesn’t really change the fact that Sondland apparently believed it to be the case.

If true, Sondland would be the third of three U.S. diplomats on those text messages turned over by Kurt Volker to point to some kind of connection between official U.S. actions and Ukraine pursuing Trump’s investigations.

This is probably Sondland’s most significant potential role in this whole situation. We’ll see how he accounts for it one day — hopefully.

2. What did Volker testify about a quid pro quo?

Despite all of the above — and despite Volker’s own text messages suggesting that he might have believed there to be a quid pro quo involving Ukraine getting a White House meeting — Republicans have been adamant that Volker’s full testimony paints a much different picture.

From very soon after his deposition started, they began suggesting he had destroyed the Democrats’ narrative. And Democrats have repeatedly urged House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) to release the full transcript, posthaste.

We do know some of what Volker said, because we’ve seen his opening statement. At one point, Volker said that “I at some stage found myself faced with a choice: to be aware of a problem and to ignore it, or rather to accept that it was my responsibility to try to fix it.” But the rest of his statement doesn’t dwell upon what that problem was.

Volker’s statement also doesn’t deal with a potential quid pro quo, though it does say “at no time was I aware of or took part in an effort to urge Ukraine to investigate former Vice President Biden.”

That’s a little difficult to swallow, given that Trump lawyer Rudolph W. Giuliani had been pushing for that very publicly for months. But it also suggests Volker didn’t waltz into his deposition and start spilling juicy tales about the internal workings of the administration. And Republicans seem to think his full testimony paints a pretty good picture — or at least that it can be used to muddy the waters sufficiently. We’ll see.

(One key point: It makes some sense for Schiff not to release Volker’s deposition before Sondland and/or Taylor testify, for fear of their versions of events being influenced by what Volker said.)

3. What kind of witness is Bill Taylor?

So we’re still waiting for Sondland’s deposition, and we’re still waiting for more information about Volker’s. But the third U.S. diplomat here, Taylor, would seem to be perhaps the best witness for Democrats.

That’s because Taylor at two separate junctures expressed reservations about military aid being tied to political favors — the one above and this one, on Sept. 1:

TAYLOR: Are we now saying that security assistance and WH meeting are conditioned on investigations?
SONDLAND: Call me.

While Volker talks in broad terms about a White House meeting being tied to the investigations, Taylor draws a more direct line. He also directly ties the investigations to Trump’s reelection campaign, directly stating that the White House was “withhold[ing] security assistance for help with a political campaign.”

That sounds a lot like someone who is righteously upset by the whole situation — and might make for a compelling witness because of it.

At the same time, it’s not clear from these texts that Taylor was working off anything besides his own suspicions. By this point, it was public knowledge that the aid was being withheld (thanks to a late August report in Politico). So Taylor might simply have been connecting the dots that we all began connecting once we knew that Trump personally pushed for investigations on that July 25 phone call with Ukraine President Volodymyr Zelensky.

Taylor, like Sondland, is a State Department employee. That means the White House will apparently fight his deposition. But it could be a very significant one if it happens.

4. How do Mike Pence and Rick Perry factor in?

The big news this weekend was that Trump has been privately blaming Energy Secretary Rick Perry for telling him to talk to Zelensky, according to Axios.

“Not a lot of people know this but, I didn’t even want to make the call,” Trump said, according to anonymous sources. “The only reason I made the call was because Rick asked me to. Something about an LNG [liquefied natural gas] plant.”

First off, that’s telling, because it suggests Trump’s claims about his “perfect” call with Zelensky mask his true concern about where it has landed him.

And second, it suggests more involvement from Perry, whose role in this is a major unknown. We knew previously that Perry was the man that replaced Vice President Pence at Zelensky’s inauguration because, according to the whistleblower, Trump didn’t want Pence to go. The Post reported that Perry will exit the administration at the end of the year. This week, Perry denied that.

Pence is also tied in with this, as The Post reported last week. He pressed Zelensky on “corruption” in their early September meeting in Poland, according to Pence. His team had emphasized that it didn’t really go beyond that, but as with Volker, it should have been pretty apparent what type of alleged “corruption” Trump was truly concerned about — the kind that serves his political purposes.

We don’t yet know much about any other Perry or Pence roles here. But especially for Pence, who would take over for a removed Trump and could be the next GOP presidential nominee, he’s got a lot of skin in this game.