A remarkable series of private text messages turned over to Congress Thursday is providing a new window into the Trump administration's dealings with Ukraine, including an extraordinary warning from America's top diplomat in Kyiv that military assistance appeared to be withheld for political purposes.

The messages were provided to congressional investigators by Kurt Volker, who resigned last week as the State Department's special envoy to Ukraine and spent hours Thursday answering questions behind closed doors as part of the House impeachment inquiry.

The exchanges involve Volker, U.S. Ambassador to the European Union Gordon Sondland, acting U.S. Ambassador to Ukraine William Taylor and Andrey Yermak, a senior adviser to Ukrainian President Volodymyr Zelensky.

They document weeks of discussions surrounding a potential White House meeting for Zelensky, Ukrainian investigations sought by President Donald Trump and his allies, and hundreds of millions of dollars in U.S. security assistance being withheld from Ukraine.

One message stands out.

“I think it's crazy to withhold security assistance for help with a political campaign,” Taylor wrote.

“Are We Now Saying” Aid Depends on Investigations?

The messages stretch from July through September and show diplomats working to arrange closer relations between Trump and Zelensky.

But as the exchanges progress, Taylor becomes increasingly concerned about what Ukraine is being asked to do.

On September 1, Taylor sent Sondland a blunt question:

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

Sondland did not answer the question by text.

Instead, he replied:

“Call me.”

The exchange is significant because the Trump administration had placed a hold on nearly $400 million in military assistance approved for Ukraine as the country continues confronting Russian-backed forces.

At the same time, Trump and his personal attorney Rudy Giuliani were pressing for investigations involving former Vice President Joe Biden, his son Hunter Biden and allegations concerning Ukrainian involvement in the 2016 U.S. election.

Joe Biden is seeking the Democratic presidential nomination and could face Trump in the 2020 election.

A Ukrainian Statement

Other messages show American diplomats discussing a public statement that Zelensky's government might issue concerning investigations.

On August 10, Yermak told Volker that once Ukraine received confirmation of a date for Zelensky to visit Washington, the Ukrainian government could hold a press briefing outlining a renewed U.S.-Ukraine relationship.

Yermak specifically mentioned “Burisma” and “election meddling in investigations.”

Hunter Biden previously served on the board of Burisma, a Ukrainian energy company.

Volker responded:

“Sounds great!”

The messages indicate that American and Ukrainian officials were negotiating both the language of an announcement and the possibility of Zelensky receiving a White House meeting.

“The Nightmare”

By early September, Taylor's concern had become unmistakable.

On September 8, Taylor discussed what he called a “nightmare” scenario.

“The nightmare is they give the interview and don't get the security assistance,” Taylor wrote.

“The Russians love it.”

He added:

“(And I quit.)”

The following day, Taylor again raised concerns about the withheld assistance.

“With the hold, we have already shaken their faith in us,” he wrote.

Then came the most striking message in the exchange.

“As I said on the phone, I think it's crazy to withhold security assistance for help with a political campaign.”

Sondland Pushes Back

Sondland responded several hours later and rejected Taylor's characterization of Trump's intentions.

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

He said Trump had been “crystal clear” that there were “no quid pro quo's of any kind” and argued that the president was attempting to determine whether Ukraine was serious about transparency and reform.

Sondland then suggested ending the discussion by text.

“I suggest we stop the back and forth by text,” he wrote.

Volker Spends Hours With Investigators

The messages emerged Thursday as Volker became the first major State Department witness to appear before congressional investigators examining Trump's dealings with Ukraine.

Volker spent roughly 10 hours behind closed doors with members and staff from the House Intelligence, Oversight and Foreign Affairs committees.

His testimony comes amid an impeachment inquiry that has rapidly expanded since House Speaker Nancy Pelosi formally announced it last week.

At the center of the inquiry is Trump's July 25 telephone conversation with Zelensky.

According to a White House memorandum of that conversation, Trump asked Zelensky to investigate matters involving Biden shortly after Zelensky raised the subject of U.S. military assistance.

Trump insists the conversation was appropriate and repeatedly describes it as a “perfect” call.

He has denied that military assistance was withheld to pressure Ukraine into conducting investigations.

Now There Is a Written Record

The newly disclosed messages do not by themselves settle the central question confronting Congress: why the Trump administration withheld security assistance from Ukraine and whether that decision was connected to investigations sought by the president.

Sondland explicitly disputed Taylor's interpretation.

But the exchanges demonstrate that senior American diplomats were discussing the possibility.

And at least one of them was deeply alarmed by it.

William Taylor wasn't a commentator watching the controversy unfold on television.

He was the top American diplomat in Ukraine.

And on September 9, he put his concern in writing:

“I think it's crazy to withhold security assistance for help with a political campaign.”

Tonight, Congress — and the American public — has that message.