Was there a quid pro quo with Ukraine? Three questions.

Editor’s note: This article was updated at 5:45 p.m. on Oct. 22 to include testimony from senior U.S. diplomat William Taylor Jr.

A key part of the House impeachment inquiry into President Donald Trump involves three Latin words: quid pro quo, literally “this for that.” Did President Trump withhold aid from Ukraine to pressure it to launch an investigation that might benefit him politically?

Democrats charge that the president abused his office by improperly leveraging U.S. foreign policy to try to dig up dirt on former Vice President Joe Biden and his son Hunter Biden and to pursue a debunked theory that Ukraine, not Russia, was behind the hacking of Democratic Party emails in 2016.

President Trump’s defenders insist that while the president may have asked the Ukrainian leader for help with certain matters, it was entirely appropriate and there was no quid pro quo. Acting White House Chief of Staff Mick Mulvaney recently complicated that argument by seeming to say there was a quid pro quo, but that’s a common feature of foreign policy – an assertion he later tried to walk back.

On Tuesday, explosive testimony from William Taylor Jr., the senior U.S. diplomat in Ukraine, added a new dimension and new urgency to the quid pro quo question. Mr. Taylor told House impeachment investigators that President Trump did withhold Ukraine aid and a promised White House meeting for Ukraine’s leader until Ukrainian officials publicly promised to investigate the Bidens, father and son.

If true Mr. Taylor’s assertions would directly contradict the president’s “no quid pro quo” stance, while calling into question the accuracy of several impeachment witnesses who have stated they were unaware of such pressure.

What did Mr. Taylor say?

Mr. Taylor was acting ambassador for the U.S. in Ukraine. His Tuesday testimony occurred behind closed doors, but news organizations obtained copies of his 15-page opening statement, which was apparently based on copious notes and memos for the record from Mr. Taylor’s files.

In short, he said that the quid pro quo was real, and drew a line directly from President Trump to the mysterious withholding of American military aid intended to help Ukraine defend against Russian incursion on its territory.

“I said on September 9 in a message to [Ambassador to the European Union] Gordon Sondland that withholding security assistance in exchange for help with a domestic political campaign in the United States would be ‘crazy’. I believed that then, and I still believe that,” Mr. Taylor said in his opening statement.

Mr. Taylor said that Mr. Sondland, a wealthy hotelier and political appointee who donated to the Trump campaign, informed him of the reasons for the unusual hold in a phone call. Everything was dependent on a public statement by Ukraine of an investigation into Biden-related matters, Mr. Sondland said, according to Mr. Taylor.

The president wanted Ukraine in a “public box,” Mr. Taylor was told. Presumably this would help ensure the investigations really occurred. It might also have been a means, by itself, of throwing doubt on the honesty of former Vice President Biden and his son.

“Ambassador Sondland tried to explain to me that President Trump is a businessman,” Mr. Taylor said in his statement. “When a businessman is about to sign a check to someone who owes him something, he said, the businessman asks that person to pay up before signing the check.”

A diplomat with five decades of experience, Mr. Taylor described a situation in which there were two channels for Ukraine policy, “one regular, and one highly irregular.” The latter consisted of Mr. Sondland, special envoy to Ukraine Kurt Volker, Energy Secretary Rick Perry, and the president’s lawyer Rudy Giuliani.

What happens now?

Democrats who heard Mr. Taylor’s testimony described it as a possible inflection point in their impeachment inquiry. Republicans were tight-lipped about what the diplomat had said.

There is sure to be a fight over Mr. Taylor’s credibility, and over the question of whether his statements really describe a direct line from the Oval Office to Ukraine, or simply his mistaken impression of what the circumstances were in this case.

One possible line of defense: GOP lawmakers are likely to describe Mr. Taylor as a bureaucrat disgruntled by the fact that the Trump administration was sapping the bureaucracy’s power and implementing new policies on its own, of which the career State Department hierarchy simply disapproved.

Democratic House investigators are almost certain to try and speak again with Mr. Sondland. In his previous appearance, compelled by a House subpoena, Mr. Sondland had said that President Trump had told him there was no quid pro quo in this instance, but he was not certain of the truth of that assertion. He also said that he did not recall having discussions with any State Department or White House official about former Vice President Biden or his son.

Would a quid pro quo be an impeachable offense?

It may all come down to Mr. Trump’s intent.

In many circumstances it is perfectly proper for a high U.S. official, even a president, to ask foreign countries for assistance with an ongoing law enforcement investigation, according to George Washington University law professor Jonathan Turley.

“Such calls can shortcut bureaucratic red tape, particularly if the evidence is held, as with this case, by national security or justice officials,” Mr. Turley wrote in an October 2 column in The Hill.

It may also be appropriate in some circumstances for a president to ask a foreign country to investigate a political rival, as President Trump appears to have done by urging the Ukrainian president to investigate the activities of former Vice President Biden and his son Hunter Biden. As Ohio State constitutional law professor Edward Foley points out in Politico, it all depends on what the rival may have been doing, and whether the president has the nation’s broader interests at heart.

In 1804, former Vice President Aaron Burr contacted the British government, looking for foreign support to cut the western portion of the U.S. away to form a separate country. President Thomas Jefferson, who detested Mr. Burr, eventually had the former vice president tried for treason. Probing this alleged deal was clearly in the country’s interest.

“Jefferson as president would have been acting responsibly if he had requested Britain’s assistance in the investigation of Burr,” Mr. Foley writes. 

In his dealings with Ukraine, including his call to investigate Mr. Biden and his son, was Mr. Trump acting for the good of the nation, or the benefit of himself? The impeachment inquiry will be tasked with answering that question. Evidence may include public statements and private discussions among staff members about possible quid pro quos.

To determine intent, lawmakers will have to judge what they believe was in Mr. Trump’s heart, as well as his actions.

“That is a tricky – but not impossible – bar for Congress to clear,” writes Mr. Foley.