WASHINGTON — A top American diplomat in Ukraine repeatedly raised concerns with colleagues about the White House’s decision to withhold $391 million in security aid from Ukraine, describing it as a “crazy” plan to withhold security assistance “for help with a political campaign,” according to texts released Thursday as part of the impeachment inquiry into President Trump.
The texts, which were turned over to Congress by Kurt D. Volker, the State Department’s former special envoy for Ukraine, come from a series of early September exchanges. They appear to show a dispute among American diplomats over whether the president was trying to use security aid or a White House meeting with the country’s new leader as leverage to pressure Ukraine to dig up dirt on a leading political rival — a charge at the heart of the impeachment investigation.
One message, written by William B. Taylor Jr., the top American diplomat in Ukraine, suggested that Mr. Trump was holding back the package of military aid to Ukraine as a bargaining chip to influence the country’s president to do his political bidding.
“As I said on the phone, I think it’s crazy to withhold security assistance for help with a political campaign,” Mr. Taylor wrote on Sept. 9 to Mr. Volker and Gordon D. Sondland, the United States ambassador to the European Union.
Mr. Sondland replied that he believed he had “identified the best path forward” for unfreezing the assistance. But he also took issue that there is any sort of direct agreement, writing in response, “The President has been crystal clear: no quid pro quo’s of any kind.” He then suggested the conversation move to phone rather than text.
The exchange and others emerged as congressional investigators met privately for more than nine hours on Capitol Hill with Mr. Volker, who is the first witness in their growing impeachment inquiry into whether Mr. Trump tried to bend American policy for his own political benefit by pressuring President Volodymyr Zelensky of Ukraine to dig up dirt on former Vice President Joseph R. Biden Jr. and other Democrats.
While the president has openly admitted that he wanted Mr. Zelensky to investigate Mr. Biden and his son Hunter Biden, a crucial question has been whether Mr. Trump tried to use the security aid or a meeting at the White House as leverage. The money was delayed until the Trump administration released it last month amid a bipartisan outcry from lawmakers.
In his text, Mr. Sondland added, “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 was not immediately clear what led Mr. Taylor to conclude that Mr. Trump was withholding aid as leverage over Ukraine. When the texts were sent, news reports about the delay in releasing the aid, and about attempts by Mr. Trump’s personal lawyer Rudolph W. Giuliani to pressure Ukraine into investigating Mr. Biden and other Democrats, had already prompted public speculation that Mr. Trump was engaging in a quid pro quo.
But his concerns persisted. Roughly a week earlier, on Sept. 1, Mr. Taylor had asked Mr. Sondland, “Are we now saying that security assistance and WH meeting are conditioned on investigations?”
Mr. Sondland replied simply, “Call me.”
The next day, Mr. Taylor described a “nightmare” situation in which the Ukrainians announced they would conduct the investigations Mr. Trump wanted and still not receive the security assistance. “The Russians love it,” he wrote of that potential outcome. “(And I quit.)”
Mr. Taylor could not be reached for comment on Thursday. The texts thrust him into the center of the blossoming controversy, and he is now almost certain to be called to testify by lawmakers.
Democrats leading the investigation said the messages “reflect serious concerns raised by a State Department official about the detrimental effects of withholding critical military assistance from Ukraine, and the importance of setting up a meeting between President Trump and the Ukrainian president without further delay.”
Republicans demanded a full transcript of Mr. Volker’s interview be released. “The facts we learned today undercut the salacious narrative that Adam Schiff is using to sell his impeachment ambitions,” wrote Representatives Jim Jordan and Devin Nunes, the top Republicans on the Oversight and Reform and Intelligence committees, referring to the chairman of the intelligence panel.
When the Trump administration forced out Marie L. Yovanovitch, the former ambassador, before her term was up, Mr. Taylor was sent to be the chargé d’affaires, the No. 2 post in an embassy, and acting ambassador. Mr. Taylor was a former ambassador in Ukraine, serving from 2006 to 2009.
The texts among Mr. Volker, Mr. Sondland and Mr. Taylor portray him as a diplomat deeply skeptical of the Trump administration’s approach to Ukraine, flabbergasted that the military assistance had been cut off — and firmly believing that the White House was asking for Ukraine to begin political investigations in return for the aid being released.
In one text, he worried about how the hold would affect Ukrainians’ view of the United States and if it would have “shaken their faith in us.”
The texts also suggest that Mr. Volker, a former ambassador to NATO, was deeply intertwined in efforts by the president and Mr. Giuliani to press the Ukrainians into action.
Mr. Volker’s name appears several times in an anonymous C.I.A. whistle-blower complaint that set off the impeachment inquiry, and Mr. Giuliani has said publicly he briefed Mr. Volker on his efforts. The complaint centers on a July call Mr. Trump had with Mr. Zelensky, in which he pressed him to investigate Mr. Biden, and asserts that Mr. Volker advised the Ukrainians on how to “navigate” Mr. Trump’s demands.
In his session with investigators, Mr. Volker presented himself as a diplomat caught in the middle “trying to solve a problem” and help Ukraine, but as someone who was not “fully in the loop” on the president’s campaign to pressure Ukraine to investigate his rivals, according to a person briefed on his testimony.
Mr. Volker told investigators that even as he agreed to set up a meeting between Mr. Giuliani and Mr. Zelensky’s top aide, he warned Mr. Giuliani that he believed the conspiracy theories Mr. Giuliani was pursuing were unfounded. While there may have been Ukrainians interested in influencing the United States government, Mr. Volker told investigators that he thought it was implausible that Mr. Biden or the Hillary Clinton campaign did anything wrong.
Mr. Volker told the committee staff that he was never informed that Mr. Trump raised Mr. Biden or the 2016 election during the July 25 phone call, nor was he shown the rough transcript afterward. He was in Ukraine at the time and met the next day with Mr. Zelensky, who he said raised no concerns about the call with him.
In his testimony, Mr. Volker told investigators he believed Mr. Taylor was a diplomat of high integrity. But he also said he did not see the freezing of the assistance as directly linked to Mr. Trump’s interest in the beginning a new Ukraine investigation as Mr. Taylor did, according to a person familiar with the testimony.
Mr. Taylor concluded that the assistance was linked to Mr. Trump’s desire for a new investigation in Ukraine based on news reports, Mr. Volker testified, according to the person. While Mr. Taylor feared the aid would never come, Mr. Volker told House investigators he was sure that Congress or the Pentagon would force the administration to release the assistance and the issue would be resolved. Mr. Volker believed if he could persuade Mr. Trump that Mr. Zelensky was trustworthy, he could push the relationship to a better place, he said in his testimony.
Mr. Volker told the committee that he did not act at Mr. Pompeo’s behest but briefed the secretary of state who approved of his actions. He also said he kept John R. Bolton, the national security adviser, informed.
The interview, which Mr. Volker participated in voluntarily, took place out of public view. The text exchange was part of a trove of more than 60 pages of documents, many of them texts, that Mr. Volker provided before he arrived.
Mr. Volker resigned on Friday from his part-time, unpaid State Department post without public explanation. A person familiar with his thinking said the longtime diplomat concluded he could no longer be effective in the post in light of the unfolding scandal. But the resignation also freed him to appear before the House investigators without restrictions, according to people familiar with his account.
Democrats are pushing their impeachment investigation forward with haste, issuing near-daily requests or subpoenas for documentary evidence and witness testimony.
The session with Mr. Volker was the first in what is expected to be a fast-paced series of interviews in the coming weeks, when Democrats aim to bring a parade of witnesses behind closed doors for questioning. Ms. Yovanovitch is expected to appear next week.
Other State Department diplomats, including Mr. Sondland, and associates of Mr. Giuliani’s are scheduled to participate, as well, but it remains to be seen whether they will appear voluntarily. Secretary of State Mike Pompeo told the committee this week that its requests were inappropriately aggressive and untenable.
Maggie Haberman contributed reporting from New York, and Lara Jakes from Washington.