It’s generally not a good sign when a government official sends a written message questioning the propriety of an action and another official replies by suggesting they talk on the phone. The implication is that the second official is worried about leaving behind evidence of their conversation. A phone call doesn’t leave a paper trail.

On Thursday night, the chairmen of the House Foreign Affairs, Intelligence and Oversight committees — Reps. Eliot L. Engel (D-N.Y.), Adam B. Schiff (D-Calif.) and Elijah E. Cummings (D-Md.), respectively — made public a document excerpting text messages exchanged between government officials working on the U.S.-Ukraine relationship. Those officials sat in positions that are currently under intense scrutiny, with still-expanding questions about President Trump’s behavior toward Ukraine and his efforts to get that country to conduct investigations that he hoped would aid him politically.

While the released text messages aren’t comprehensive (representing “only a subset of the full body of the materials,” according to the letter accompanying the messages) and don’t directly implicate Trump, they contain significant revelations and suggestions about the Trump-Ukraine interactions. They include, in two suggestive moments, specifically the sort of don’t-document-this responses that imply an awareness of lines being crossed.

Rep. Eric Swalwell (D-Calif.) and Rep. Mark Meadows (R-N.C.) comment on Ukraine diplomat Kurt Volker's Oct. 3 impeachment inquiry deposition. (Reuters)

1. There’s an explicitly stated quid pro quo.

A central participant in the messages is Kurt Volker, former special envoy to Ukraine. Until last week, he served in the administration, resigning shortly after he was identified in a complaint filed by a whistleblower in the intelligence community. The whistleblower portrayed Volker as working with European Union Ambassador Gordon Sondland to try to run interference between Ukrainian officials and Trump’s personal attorney Rudolph W. Giuliani, who was pressing for Ukraine to investigate former vice president Joe Biden.

The text messages suggest that Volker and Sondland might more accurately be described as trying, at times, to effect what Giuliani — and Trump — wanted to see: an investigation into a completely unfounded attempt to link Ukraine to the hacking of the Democratic National Committee network in 2016 and a probe of Biden and work his son Hunter did for an energy company called Burisma Holdings. The Trump-Giuliani theory is that Joe Biden wanted Ukraine to fire its general prosecutor to protect Hunter and Burisma; there remains no significant evidence that this happened.

On July 21, four days before Trump and Ukrainian President Volodymyr Zelensky had a phone call in which Trump asked Zelensky to conduct precisely those investigations, Sondland had a text message exchange with Bill Taylor, the acting U.S. ambassador in Ukraine. Taylor made clear that Zelensky wanted “Ukraine [to be] taken seriously” and not just serve as “an instrument in Washington domestic, reelection politics.” Part of that, it is later revealed, is getting Zelensky an invitation to meet Trump in Washington.

Shortly before the call on July 25, Volker texted Andrey Yermak, an adviser to Zelensky (who had been inaugurated two months prior). In that message, Volker was explicit about what it would take to get that meeting.

“Heard from White House,” Volker wrote, “assuming President Z convinces trump he will investigate / ‘get to the bottom of what happened’ in 2016, we will nail down date for visit to Washington.”

This is as explicit a quid pro quo as you can get: Promise to get to the bottom of events in 2016 — which could refer to either the hacking or to the firing of a Ukrainian prosecutor targeted by Biden — and you’ll get the validity that comes with a White House visit.

What’s not clear is who Volker spoke with in the White House. In the call between Trump and Zelensky later that day, the meeting was raised, with Trump vaguely suggesting that Zelensky could pick his dates only after the Ukrainian leader had promised to go along with the politically useful investigations Trump wanted to see.

The extent to which that visit was important to Zelensky was highlighted when he and Trump met on Sept. 25 on the sidelines of the U.N. General Assembly.

“I want to thank you for the invitation to Washington,” Zelensky said. “You invited me, but I think — I’m sorry. I’m sorry. But I think you forgot to tell me the date.”

People in attendance laughed. Trump looked annoyed and pointed to someone standing nearby. “They’ll tell you the date,” Trump said.

“Oh, yes, they know before us,” Zelensky replied.

2. The U.S. helped shape a statement from Ukraine mentioning the Biden probe.

In a text message exchange with Volker immediately after the call, Zelensky’s aide Yermak suggested Sept. 20 through 22. By early August, though, those dates hadn’t been confirmed.

In an exchange with Volker on Aug. 9, Sondland suggested that dates would be finalized as soon as Yermak confirmed … something. From the context of Sondland’s comments in the thread, it seems that the something is a written statement that would accompany a news conference by Zelensky, presumably to announce the new investigations.

Asked how he got the White House to finally agree to set dates, Sondland suggested that it isn’t final yet: “I think potus really wants the deliverable” — again presumably that statement. Shortly after that exchange, Volker contacted Giuliani to get guidance on what the statement should include.

The next day, Volker and Yermak corresponded by text message with Yermak, with the aide insisting that dates for a visit be set before the statement was released.

“Once we have a date,” the Zelensky aide wrote, “will call for a press briefing, announcing upcoming visit and outlining vision for the reboot of US-UKRAINE relationship, including among other things Burisma and election meddling in investigations.”

Again, an investigation into Burisma is, in essence, an investigation into Hunter Biden’s work and an effort to position Joe Biden as having acted unethically. Yermak was promising to uphold his end of the quid pro quo, once a date is set.

On Aug. 13 — coincidentally the day after the whistleblower complaint was filed — Volker sent Sondland what appears to be draft language to include in the statement.

“Special attention should be paid to the problem of interference in the political processes of the United States especially with the alleged involvement of some Ukrainian politicians,” the text read — an additional reference to the release of information implicating then-Trump campaign manager Paul Manafort in illegal payments in August 2016.

“I want to declare that this is unacceptable,” Volker wrote, presumably speaking as though he’s Zelensky. “We intend to initiate and complete a transparent and unbiased investigation of all available facts and episodes, including those involving Burisma and the 2016 U.S. elections, which in turn will prevent the recurrence of this problem in the future.”

“Perfect,” Sondland replied.

Four days later, Sondland asked whether they still want Burisma and the 2016 elements in the statement.

“That’s the clear message so far,” Volker replied.

But the statement doesn’t happen. It’s not clear why it didn’t — although it may again be because no date for a meeting with Trump was set.

3. There’s a strong suggestion that military aid was used as leverage — and hints at an attempt to hide that.

By the end of August, the Ukrainians had learned that the United States is withholding military aid, a decision made by Trump before the July 25 call. Trump had been scheduled to travel to Poland for an international event but, with Hurricane Dorian threatening Florida and Georgia, he remained in the United States. Vice President Pence went in Trump’s stead and was slated to meet with Zelensky on Sept. 1.

A bit after noon on that day, Taylor, the U.S. official in Ukraine, texted Sondland.

“Are we now saying that security assistance and WH meeting are conditioned on investigations?” Taylor asked.

“Call me,” Sondland replied. And their conversation on that central point was not recorded.

Taylor’s question is a central one to the Trump-Ukraine interaction. There are significant problems that arise if Trump tried to leverage his position and America’s interests to get Ukraine to investigate his political opponents. There are larger problems that arise if Trump halted congressionally approved funding to use it as leverage.

On Sept. 8, Volker, Taylor and Sondland tried to get on the phone, but Volker couldn’t hear the conversation.

“Gordon [Sondland] and I just spoke,” Taylor texted Volker. “I can brief you if you and Gordon don’t connect.” Taylor continued: “The nightmare is they give the interview and don’t get the security assistance. The Russians love it. (And I quit.)”

Taylor’s reference to “the interview” isn’t clear, but he probably means the press announcement about imminent investigations. Taylor was apparently worried that Ukraine would give the interview but the United States would still withhold aid, to Russia’s glee.

Early the next morning, Taylor again raised his concerns with Sondland.

“The message to the Ukrainians (and Russians) we send with the decision on security assistance is key,” he said. “With the hold [on the assistance], we have already shaken their faith in us. Thus my nightmare scenario.”

Sondland replied, saying that he “believe[s] we have identified the best pathway forward.”

“As I said on the phone,” Taylor replied, apparently referring to the failed three-way call on Sept. 8, “I think it’s crazy to withhold security assistance for help with a political campaign.”

Five hours later, Sondland replies — using very pointed language.

“Bill, I believe you are incorrect about President Trump’s intentions,” he wrote. “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.”

It’s hard to read that reply, with its unusual formality and detail, as anything other than an attempt to establish a particular argument for the written record.

“I suggest we stop the back and forth by text,” he added, reinforcing that interpretation. “If you still have concerns I recommend you give Lisa Kenna” — the State Department’s executive secretary — “or S” — perhaps the secretary of state — “a call to discuss them directly. Thanks.”

No further text messages were shared.