Thursday brought new bombshells in the Ukraine case, as Trump’s former envoy to Ukraine, Kurt Volker, who was forced to resign last week, gave a deposition to House investigators. Republicans who were present insisted that Volker had not said there was a quid pro quo for dirt on Biden, but you don’t have to take their word for it, because the Democratic chairs of three committees released text messages that Volker turned over.

The messages make clear that both American and Ukrainian officials understood that there was a quid pro quo: If Zelensky wanted to get a White House visit and military aid, he had to manufacture an investigation into the Bidens. In one message, Volker wrote that “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.” Trump’s ambassador to the European Union, Gordon Sondland wrote, “i think potus really wants the deliverable.”

In another exchange, Bill Taylor—a career Foreign Service officer and the top U.S. diplomat in Ukraine after the ambassador was fired, reportedly at Giuliani’s behest—wrote, “Are we now saying that security assistance and WH meeting are conditioned on investigations?” Sondland, evidently worried about creating a paper trail, instructed Taylor to call him.

A few days later, Taylor said, “I think it’s crazy to withhold security assistance for help with a political campaign.” After taking five hours to reply, Sondland again tried to clean up matters and prevent any written record. “Bill, I believe you are incorrect about President Trump’s intentions. The President has been crystal clear no quid pro quo’s of any kind,” he wrote, adding, “I suggest we stop the back and forth by text.” Sondland also recommended that Taylor contact the secretary of state if he had other questions, making Mike Pompeo’s involvement in the scheme clear.

But the stain of scandal is spreading, as a steady drip of evidence shows that Trump has sought to gather dirt on Biden from friends and adversaries alike, across the globe.

David A. Graham: What happened in Ukraine?

Thursday morning on the White House’s South Lawn, Trump told reporters that China should mount a probe: “They should investigate the Bidens, because how does a company that’s newly formed—and all these companies—and by the way, likewise, China should start an investigation into the Bidens because what happened in China is just about as bad as what happened with Ukraine.” There is no evidence to back up his charges. The moment was breathtaking, because Trump, under threat of impeachment for asking a foreign country to interfere in the 2020 election, opted to ask a foreign country to interfere in the 2020 election, with cameras rolling.

Once again, there’s a quid pro quo on the table. China and the U.S. are fighting a trade war and are engaged in tense negotiations about trade policy, giving Beijing every reason to mount a probe to curry favor with Trump. As it turns out, this wasn’t Trump’s first request to China to investigate the Bidens. CNN revealed Friday night that in a June call with President Xi Jinping, Trump had brought up Biden. Trump also promised Xi not to bring up pro-democracy protests in Hong Kong during trade negotiations, which explains Trump’s bizarre silence on the demonstrations but spotlights his conciliatory negotiating approach and his lack of commitment to democratic principles.