WASHINGTON (Reuters) – U.S. Ambassador to the European Union Gordon Sondland acknowledged telling a top Ukrainian official that U.S. security assistance withheld by President Donald Trump was unlikely to be delivered until Ukraine publicly met a demand for an “anti-corruption” statement, according to a new declaration from Sondland released on Tuesday. Sondland initially testified in October to a Democratic-led impeachment inquiry of Trump in Congress, and offered new details to lawmakers on Monday after his memory was “refreshed,” that appear to bolster the initial whistleblower complaint that led to the investigation. Sondland’s testimony also corroborates those of other witnesses, who have said Trump sought to pressure the Ukrainians into conducting investigations that appeared to be aimed at helping his re-election campaign. The impeachment inquiry in the U.S. House of Representatives is focused on a July 25 phone call in which Trump asked Ukrainian President Volodymyr Zelenskiy to open an investigation into former U.S. Vice President Joe Biden and his son Hunter Biden. Joe Biden is a leading contender for the Democratic Party nomination to run against Trump in the November 2020 election. Hunter Biden was on the board of a Ukrainian gas company that had been investigated for corruption. Sondland sent a text message in September in which he said Trump insisted there was “no quid pro quos.” Related CoverageU.S. ambassador to EU saw quid-pro-quo in call for Ukraine corruption probe: excerptsU.S. House committees seek deposition with Trump chief of staff Mulvaney in impeachment probeSondland said in his new statement that by the beginning of September “in the absence of any credible explanation” he concluded that the nearly $400 million in withheld aid was linked to Trump’s demand that Ukraine publicly acknowledge an investigation. Sondland has said he didn’t realize early on that the investigation was meant to target the Bidens. “Resumption of U.S. aid would likely not occur until Ukraine provided the public anti-corruption statement that we had been discussing for many weeks,” Sondland said he told a Ukrainian presidential adviser. Much of the early parts of the investigation by three House committees that include Democratic and Republican lawmakers, were conducted behind closed doors, but now the inquiry is moving into a public phase with the release of testimony and anticipated on-camera interviews in the next month. Sondland submitted the supplemental testimony on Monday after statements by other officials, including Bill Taylor, the top U.S. envoy in Ukraine. Trump has denied wrongdoing and accused Democrats of unfairly targeting him in hope of reversing his surprise victory in the 2016 presidential election. Democrats accuse Trump of misusing taxpayer dollars destined for a vulnerable U.S. ally for personal political gain. If the House votes to approve articles of impeachment – formal charges – the Republican-controlled Senate would then hold a trial on whether to remove the president from office. Senate Republicans have so far show little appetite for removing the president. “If it were today, I don’t think there’s any question it would not lead to a removal,” Senate Republican leader Mitch McConnell told reporters on Tuesday, adding that the duration of any trial would depend on how long senators want to take. Congressional Democrats also released testimony from Kurt Volker, Trump’s former special representative for Ukraine negotiations. In his testimony Volker detailed what he described as the role of Trump’s personal lawyer Rudy Giuliani as a conduit between Washington and Kiev. He also said his decision to resign on Sept. 27 was because of the impeachment inquiry. “I didn’t think I would be able to go to Ukraine or meet with Russians and be able to carry out those duties in that way anymore,” he said. He also said he wanted to provide testimony “with as much candor and integrity as I possibly could.” Witnesses have testified that Volker and Sondland, with Trump’s secretary of energy, Rick Perry, were known as the “three amigos,” responsible for Trump’s unofficial channel to Ukrainian government officials. Volker resigned as special representative in September. He testified to the House Foreign Affairs, Intelligence and Oversight panels for more than eight hours behind closed doors on Oct. 3. Perry, a former Texas governor who said he was resigning from his Cabinet post as of Dec. 1, has refused to testify so far.