A political battle over a classified whistleblower complaint about U.S. President Donald Trump escalated on Friday, with Democrats warning of a national security threat and Republicans turning it into an attack on Joe Biden, one of Trump’s chief political rivals. Trump dismissed the complaint from a whistleblower within the intelligence community – reported by several U.S. news organizations to involve the Republican president’s communications with a foreign leader – as a partisan hit against him. The Sept. 12 complaint centered on Ukraine, the Washington Post reported. Reuters has not confirmed details of the whistleblower’s complaint. But a source familiar with the matter said it alleged “multiple acts” by Trump, not just a phone call with a foreign leader. The source requested anonymity because of the sensitivity of the issue. Trump had spoken with Ukraine’s recently elected president, Volodymyr Zelenskiy, less than three weeks before the complaint was filed. Trump is due to meet Zelenskiy during a United Nations gathering in New York. The July 25 call between the leaders is under investigation by three Democratic-led House committees, who want to know if Trump and his personal lawyer, Rudolph Giuliani, tried to pressure the Ukrainian government into aiding Trump’s re-election campaign. Giuliani said on CNN on Thursday he had asked the Ukrainian government to investigate Hunter Biden, the son of former Vice President Biden, who is a frontrunner in the field of Democrats seeking to challenge Trump in the 2020 presidential election. Giuliani alleged that as vice president, Biden sought the firing of a Ukrainian prosecutor who was investigating his son’s business dealings. Biden and his son have denied the charge. Biden’s campaign did not immediately respond to a request for comment on Friday. The former prosecutor, Viktor Shokin, had been criticized by the U.S. government and the European Union for larger issues, including blocking reforms to Ukraine´s legal system. Ukraine’s parliament approved his dismissal in March 2016. On Friday, Giuliani was seen by Reuters reporters at the Trump International Hotel, a few blocks away from the White House, sitting next to Lev Parnas, a Ukrainian businessman with whom Giuliani has recently been working. Giuliani declined comment. In a Sept. 9 letter to White House Counsel Pat Cipollone requesting documents, the chairmen of the House foreign affairs, intelligence and oversight committees said the Ukrainian government’s readout of Trump’s call appeared to show that he encouraged Zelenskiy to pursue the Biden investigation.