House Foreign Affairs Committee members Rep. Gerry Connolly and Tom Malinowski are also interested.

“It certainly is on the list of inquiries to be pursued,” Connolly told POLITICO on Tuesday, saying the question of potential “extortion” of Ukraine will be “a major part of the impeachment inquiry.”

“I intend to ask about it,” added Malinowski.

Trump’s July 25 phone call with Zelensky—in which he urged him to investigate his political rival Joe Biden and issues surrounding the 2016 election, all while withholding military assistance aid to Kiev—and the concurrent pressure placed on Zelensky by U.S. diplomats has led some Democrats to view the Javelin sale in a new light.

The U.S. completed its shipment of Javelin anti-tank missiles to Ukraine in May 2018, finalizing a sale that was pushed by lawmakers in both parties and reluctantly approved by Trump in November 2017. In April 2018, then-Ukrainian President Petro Poroshenko ordered Ukraine’s top anti-corruption prosecutor Yuriy Lutsenko—who’d been tasked with investigating corruption that occurred under former Ukrainian President Viktor Yanukovych—to stop cooperating with special counsel Robert Mueller.

Mueller, at that point, was investigating former Trump campaign chairman Paul Manafort’s work for Yanukovych in Ukraine and his ties to Russia.

Democratic Sens. Dick Durbin, Bob Menendez and Patrick Leahy sent a letter to Lutsenko on May 4, 2018, expressing their “great concern” about reports that the investigation had been impeded—and asking directly whether “any individual from the Trump administration, or anyone acting on its behalf” encouraged Ukrainian government or law enforcement officials not to cooperate with the Mueller probe. They never received a response, according to a spokesman for Democrats on the Senate Foreign Relations Committee.

Lutsenko, who met with Trump's personal lawyer Rudy Giuliani earlier this year as part of Giuliani's ongoing efforts to investigate what he claims is Ukraine's "interference" in the 2016 election, has not replied to multiple requests for comment in recent days. The White House did not reply to questions about the Javelin sale.

There was no evidence at the time that Trump had directly asked the Ukrainians to halt the cooperation, and a New York Times report indicated that the Ukrainians had done it of their own volition to stay on the president’s good side.

A person familiar with the matter said refraining from selling Javelins to Ukraine had been “a bad policy in the Obama administration” that top Trump administration officials including then-Defense Secretary Jim Mattis and then-Secretary of State Rex Tillerson were eager to reverse. (The Obama administration’s hesitance to approve the sale of the Javelins, officials said at the time, was primarily due to their concern that Russia, which was pouring troops and weapons into eastern Ukraine, could use the missiles as a pretext to escalate the conflict.)

The source acknowledged that it “took a few rounds for the president to get his support” before he signed off on it, but said he “wasn’t aware of anything related to Mueller at that time.”

Still, other sources said at the time that Trump wasn’t looking to sell the Javelins to the Ukrainians for nothing. To get him on board, Trump’s national security advisers emphasized that this would be a sale, not a gift, said a U.S. official with direct involvement in the matter. And Poroshenko won favor with Trump by facilitating an $80 million coal deal—the first between the U.S. and Ukraine—that was politically expedient for both leaders. Less than two months after the State Department approved the sale, Ukrainian Railways signed a $1 billion locomotive deal with GE Transportation, which boosted Trump’s campaign promise to revitalize the U.S. rail industry.

Now, Democrats want to know if there were other incentives at play—especially in light of Zelensky’s comment, in his July call with Trump, that Ukraine is almost ready to buy additional Javelins from the U.S. “for defense purposes.” Trump responded by asking for “a favor”—namely, that Zelensky investigate Ukraine’s involvement in the 2016 election, with help from the Attorney General.

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“When you look at the chronological order on how all these things came forward … I think it would lead anyone who’s simply trying to gather the facts to want to try to get all the information possible and see where it leads,” said Costa.

Democrats on the three panels leading the Trump impeachment inquiry—House Foreign Affairs, House Intelligence, and House Oversight—asked Kurt Volker, the former U.S. envoy to Ukraine, about Manafort and the Javelin sales during his deposition last week, according to a person familiar with his testimony. But this person couldn’t recall whether the Democrats specifically asked whether there had been a quid pro quo.

Trump and his personal lawyer, Rudy Giuliani, have continued to support Manafort, who is currently serving a 7.5-year prison sentence for tax and financial fraud crimes.

The president has defended his former campaign chairman whom he had a joint defense agreement—as a “good man” and has said he feels “badly” for him, calling his conviction “a very sad situation.” And Giuliani, who has long maintained that Manafort was framed by falsified documents, has reportedly continued to communicate with Manafort through his lawyer as he continues investigating the conspiracy theory that Ukraine, rather than Russia, interfered in the 2016 election to bring Trump and Manafort down.

Russia has been making a similar accusation since December 2016, when Russia’s Foreign Ministry spokesperson accused Ukraine of trying to sabotage Trump’s campaign by exposing a “black ledger” revealing that Manafort hid millions in payments for his work for Yanukovych. That ledger became public in August 2016 via the New York Times, and led to Manafort’s resignation as campaign chairman that month.

Manafort began pushing the White House and RNC to allege “collusion” between Ukraine and Democrats in the spring of 2017 to distract from the ongoing Russia investigation, POLITICO first reported. But prosecutors had Manafort’s financial records, not just the so-called ledger, and even Giuliani acknowledged that he didn’t think he could fully “exonerate” the disgraced Republican operative.

“This is a large puzzle that we’ve been dealing with now for the better part of three years and more recently it seems like we’re finding more pieces of the puzzle,” said Costa.