As of Wednesday night, everyone was speculating about which foreign country President Trump might have made a “promise” to — a commitment that prompted a U.S. intelligence community whistleblower to lodge a mysterious complaint.

The answer to that question is an ominous one for Trump and his supporters when it comes to what lies ahead. And that goes particularly for his 2020 reelection bid, even as we still know very little about the actual complaint.

The Washington Post broke the story late Wednesday that the whistleblower’s complaint dealt with the president and a “promise” he made to a foreign leader. And as The Post’s Ellen Nakashima, Shane Harris, Greg Miller and Carol D. Leonnig again scooped Thursday night, the complaint is focused on Ukraine:

A whistleblower complaint about President Trump made by an intelligence official centers on Ukraine, according to two people familiar with the matter, which has set off a struggle between Congress and the executive branch.
The complaint involved communications with a foreign leader and a “promise” that Trump made, which was so alarming that a U.S. intelligence official who had worked at the White House went to the inspector general of the intelligence community, two former U.S. officials said.
Two and a half weeks before the complaint was filed, Trump spoke with Ukrainian President Volodymyr Zelensky, a comedian and political newcomer who was elected in a landslide in May.

That phone call took place July 25, and for a host of reasons — and depending on the substance of the complaint — it could spell real trouble for Trump and his supporters.

The main reason is because we already knew about demonstrated and very public interest from the Trump team in what Ukraine could provide them when it comes to Trump’s reelection effort. Trump lawyer Rudolph W. Giuliani has publicly urged the Ukrainians to pursue investigations that he has admitted would benefit Trump, and one in particular that could damage what appears to be Trump’s most threatening potential 2020 Democratic opponent, Joe Biden.

In May, Giuliani canceled a controversial planned trip to Ukraine that he had admitted was intended to apply pressure on its government to investigate Biden’s son Hunter Biden and his work for a Ukrainian gas company that had previously been of interest to investigators in the country.

Giuliani even acknowledged before the planned trip that it was intended to help Trump and that Giuliani was “meddling” in foreign affairs to that end.

“We’re not meddling in an election; we’re meddling in an investigation, which we have a right to do,” Giuliani told the New York Times’s Kenneth P. Vogel. Giuliani added: “There’s nothing illegal about it. Somebody could say it’s improper. . . . I’m asking them to do an investigation that they’re doing already and that other people are telling them to stop. And I’m going to give them reasons why they shouldn’t stop it because that information will be very, very helpful to my client, and may turn out to be helpful to my government.”

It was a remarkable admission at the time — particularly that it could be “very, very helpful to my client” and separating that from the idea that it might also happen to benefit the U.S. government. And it’s even more remarkable in this moment.

When Giuliani canceled the trip, he blamed the Ukrainian government and suggested Democrats had overblown the situation.

“I’m convinced from what I’ve heard from two very reliable people tonight that the president [Zelensky] is surrounded by people who were enemies of the president [Trump], and people who are — at least [in] one case — clearly corrupt and involved in this scheme,” Giuliani told Fox News.

Rep. Adam B. Schiff (D-Calif.) on Sept. 19 said a whistleblower complaint to the intelligence community met the threshold requiring notification of Congress. (JM Rieger/The Washington Post)

We know basically nothing about what the whistleblower says Trump might have made a “promise” about or discussed about Ukraine, or even whether it specifically involved that July 25 phone call with Zelensky, which came two and a half weeks before the whistleblower complaint was filed Aug. 12.

But the Ukrainian government’s readout of that call mentioned how Trump was “convinced the new Ukrainian government will be able to quickly improve [the] image of Ukraine, [and] complete [the] investigation of corruption cases, which inhibited the interaction between Ukraine and the USA.”

While all this was happening, the Trump administration was holding back military aid to Ukraine. In late August, it was reported that lawmakers were concerned that the administration was failing to provide $250 million for the Ukraine Security Assistance Initiative, which is intended to help Ukraine defend itself from Russia. Last week, the administration relented to bipartisan pressure and released the funds.

Whether because of those details or because he knows what happened, Giuliani appeared on CNN on Thursday night and defended Trump as if there were some kind of a quid pro quo involving foreign aid and investigating the Bidens. (Giuliani will often be dispatched to head off bad stories for Trump, though sometimes he doesn’t have his facts straight.)

“The reality is the president of the United States has every right to say to another leader of a foreign country, ‘You got to straighten up before we give you a lot of money,’ ” Giuliani said. “It is perfectly appropriate for [Trump] to ask a foreign government to investigate this massive crime that was made by a former vice president.”

He tweeted the same sentiment shortly thereafter, despite the allegations involving the Bidens being highly speculative and far from proved.

Over the last 36 hours, speculation about the countries to which Trump might have made problematic promises has focused on Russia, to which Trump disclosed highly classified information in a 2017 Oval Office meeting and has sought curiously friendly relations, and North Korea, with which Trump has pursued an elusive nuclear deal and made significant diplomatic concessions. If Trump made any quid pro quos with either, given their statuses as antagonistic foreign powers and even enemies, it would have been bad.

But when it comes to countries with which such a “promise” might have been particularly self-serving for Trump, Ukraine is near the top of the list.