Texts show how US officials worked to prod the Ukrainian president into opening a public inquiry into President Trump’s leading opponent, Joe Biden.
The messages, released by congressional Democrats, emerge as Mr Trump faces an impeachment inquiry over the matter.
The exchanges show a senior diplomat saying it would be “crazy” to withhold military aid to Ukraine for Mr Trump’s political gain in the 2020 election.
US law bans soliciting foreign help for electoral purposes.
But Mr Trump denies any wrongdoing and, on Thursday, publicly called on Ukraine and China to investigate Mr Biden and his son Hunter over their political and business dealings, even though he has not offered specific evidence of misconduct.
The Republican president accuses his political opponents of a “witch hunt”.
Impeachment in the Democratic-controlled House of Representatives would trigger a trial in the Senate.
Senators would have to vote to convict Mr Trump by a two-thirds majority to remove him from office.
But that outcome is seen as unlikely given that the president’s fellow Republicans control the upper chamber.
The impeachment inquiry stems from a 25 July call in which Mr Trump asked President Volodymyr Zelensky to investigate his rival.
The wide-ranging text message discussions are connected to allegations by the Democrats that Mr Trump dangled military aid as a way to press Ukraine to dig dirt on Mr Biden.
Sent between July and September, they involve high-ranking officials:
Kurt Volker, Mr Trump’s Ukraine envoy who resigned a week ago
Gordon Sondland, the US ambassador to the European Union, and a significant donor to Mr Trump
Bill Taylor, a top US diplomat at the American embassy in Ukraine
On 19 July, the three diplomats discussed arranging a phone call between Mr Zelensky and Mr Trump.
Mr Volker told the other two he had had breakfast with Mr Trump’s lawyer, Rudy Giuliani that morning – and identified the main purpose of the upcoming phone call.
“Most impt [important] is for Zelensky to say that he will help the investigation,” he told the others.
But Bill Taylor, the senior US diplomat in Ukraine, warned that President Zelensky “is sensitive” about Ukraine being seen “as an instrument in Washington domestic, re-election politics”.
Ahead of the call, Mr Volker texted that he had heard from the White House that Mr Zelensky would be offered a formal visit to Washington “assuming President Z convinces Trump he will investigate / ‘get to the bottom of what happened in 2016′”.
This is a reference to unfounded allegations that Ukraine interfered in the 2016 US presidential election and worked to help the Democrats.