At the end of the day, the specific question of “quid pro quo” doesn’t matter much in the question of impeaching President Trump. Impeachment is politics, loosely predicated on wrongdoing. If Congress determines that an action is impeachable, it’s impeachable.

That said, the impeachment inquiry targeting Trump is specifically focused on his interactions with Ukraine and, secondarily, whether he withheld aid or a meeting with Ukrainian President Volodymyr Zelensky to force Zelensky to announce new investigations into Russian interference in the 2016 U.S. election or into former vice president Joe Biden.

Trump’s obvious and open requests that Zelensky open those investigations, requests documented in the rough transcript released by the White House last month, are by themselves questionable. It’s illegal to solicit foreign assistance for a political campaign, and Trump’s insistence that he wanted a probe of Biden because he’s worried about corruption in Ukraine and not because he wants to damage a possible 2020 opponent has not been universally accepted as believable. That Trump may have leveraged congressionally approved aid or the power of his position to get an announcement of investigations that would be politically useful is another thing entirely.

Evidence that Trump and his team did exactly that keeps mounting. On Thursday, Tim Morrison — until this week a special assistant to Trump — will testify before the House impeachment inquiry and reportedly confirm prior testimony in which an explicit quid pro quo was alleged. By itself that’s remarkable. But at this point it’s simply a few more logs tossed into an already raging bonfire.

There are, by our count, at least eight instances in which an explicit quid pro quo has been alleged publicly, even setting aside acting White House chief of staff Mick Mulvaney’s assertion to that end earlier this month. Four of those instances have been corroborated by additional witnesses according to media reports, including two instances involving Morrison.

Here are those eight instances.

During a meeting July 10 at the White House, E.U. Ambassador Gordon Sondland told Ukrainian officials, including Oleksandr Danylyuk, that a meeting between Trump and Zelensky depended on the initiation of investigations.

“Ambassador Sondland started to speak about Ukraine delivering specific investigations in order to secure the meeting with the president,” Lt. Col. Alexander Vindman, a member of Trump’s National Security Council, told investigators this week, “at which time Ambassador Bolton cut the meeting short.” Bolton is John Bolton, Trump’s former national security adviser.

This version of events was not corroborated by Sondland during his testimony. It was, however, reportedly confirmed by Fiona Hill, Morrison’s immediate predecessor in the administration.

After Bolton halted the meeting with the Ukrainians, the group held a separate meeting intended to debrief. At that meeting, Sondland reportedly reiterated his assertion.

“Ambassador Sondland emphasized the importance that Ukraine deliver the investigations into the 2016 election, the Bidens, and Burisma,” Vindman said. (Burisma is a Ukrainian energy company for which Biden’s son Hunter worked.) This second meeting was similarly confirmed by Hill but not Sondland.

On July 25, Trump and Zelensky spoke on the phone. This was the call in which Trump explicitly requested the investigations referred to by Sondland.

Sondland and Trump spoke on the phone before the Trump-Zelensky call. In the same period, Kurt Volker, then a special envoy to Ukraine, texted Andrey Yermak, an aide to Zelensky. In the message, which he provided to investigators, Volker explicitly linked a meeting to those investigations.

“Heard from White House — assuming President Z convinces trump he will investigate / ‘get to the bottom of what happened’ in 2016, we will nail down date for visit to Washington,” he wrote.

The meeting wasn’t set immediately. In early August, Trump’s team began trying to leverage a meeting in exchange for a public statement from Zelensky confirming new investigations. On Aug. 10, Yermak texted Volker and linked the two specifically.

“I think it’s possible to make this declaration and mention all these things [w]hich we discussed yesterday,” Yermak wrote. “But it will be logic to do after we receive a confirmation of date.”

Meeting date first, Yermak is saying — then the announcement.

About a week before the July 25 call, Trump halted aid slated to be delivered to Ukraine by Congress. By early August, some Ukrainian officials were already aware that the aid was being held.

On Aug. 30, Sen. Ron Johnson (R-Wis.) spoke with Sondland.

“Under the arrangement, Mr. Johnson said Mr. Sondland told him, Ukraine would appoint a strong prosecutor general and move to ‘get to the bottom of what happened in 2016 — if President Trump has that confidence, then he’ll release the military spending,’ ” Johnson told the Wall Street Journal.

Johnson was planning a trip to Ukraine. The next day he asked Trump about Sondland’s claim and whether he could inform Zelensky that the aid was coming. Trump said there was no quid pro quo — but also that aid was being withheld because he wanted to know the truth of what happened in 2016.

On Sept. 1, Morrison and acting Ukraine ambassador William B. Taylor spoke on the phone. Morrison briefed Taylor on a meeting that day between Vice President Pence and Zelensky in Poland.

“During this same phone call I had with Mr. Morrison, he went on to describe a conversation Ambassador Sondland had with Mr. Yermak at Warsaw,” Taylor testified. “Ambassador Sondland told Mr. Yermak that the security assistance money would not come until President Zelensky committed to pursue the Burisma investigation.”

Morrison reportedly will confirm this claim in his testimony.

After speaking to Morrison, Taylor called Sondland. In that call, Taylor claims that Sondland not only confirmed a link between aid and investigations but also said that he’d been overly narrow in what he presented to Ukrainian officials in a meeting in July — presumably the July 10 meeting. It wasn’t just a meeting that was predicated on an investigation but “everything.”

A few days later, Morrison and Taylor spoke again. In that call, Morrison claimed to have learned about another interaction between Sondland and Trump.

“According to Mr. Morrison, President Trump told Ambassador Sondland that he was not asking for a ‘quid pro quo,’ ” Taylor testified. “But President Trump did insist that President Zelensky go to a microphone and say he is opening investigations of Biden and 2016 election interference, and that President Zelensky should want to do this himself.”

Morrison is expected to confirm this conversation as well.

Two days later, on Sept. 9, Taylor texted Sondland.

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

Sondland replied five hours later, after speaking with Trump.

“Bill, I believe you are incorrect about President Trump’s intentions,” he wrote. “The President has been crystal clear no quid pro quo’s of any kind. The President is trying to evaluate whether Ukraine is truly going to adopt the transparency and reforms that President Zelensky promised during his campaign."

He then added, “I suggest we stop the back and forth by text."