* Reports that Trump urged a foreign leader to investigate Joe Biden have rocked Washington and intensified calls for impeachment * Live blog: Democrats ramp up pressure over UkraineDonald Trump at the United Nations in New York on Monday. Photograph: Jonathan Ernst/ReutersDonald Trump is facing on one of the most perilous periods of his historically perilous presidency.Reports that he urged a foreign leader to investigate Joe Biden, seen as his main rival in the 2020 presidential election, have rocked Washington and intensified calls for Trump to be impeached.Trump is set to meet Ukraine’s president, Volodymyr Zelenskiy, the leader in question, in New York on Wednesday.On Thursday, Democrats on the House intelligence committee will grill Joseph Maguire, the acting director of national intelligence. Maguire has refused to release details of a whistleblower’s complaint said to relate to a phone call between Trump and Zelenskiy, despite intensifying calls from Democrats and even some Republicans. How did this begin?A whistleblower, working in US intelligence, filed a formal complaint in August. The unnamed whistleblower is said to have seen or heard something that raised “urgent concern”.Reporting has since revealed that the complaint was based on a series of events, including a 25 July call between Trump and Zelenskiy. Complaints of this nature are usually reported to Congress within seven days. Maguire, who was appointed by Trump, has refused to do so. What happened on the call?Numerous news outlets have reported that Trump pressured Zelenskiy to investigate Joe Biden’s son, Hunter Biden, who served on the board of a Ukrainian energy company. According to the Wall Street Journal, Trump asked Zelenskiy eight times to investigate Hunter Biden.On Sunday, Trump confirmed he discussed the Bidens with Zelenskiy, and accused the pair – without offering any evidence – of corruption.“The conversation I had was largely congratulatory, was largely corruption, all of the corruption taking place,” he said. “Was largely the fact that we don’t want our people, like Vice-President Biden and his son, [contributing] to the corruption already in the Ukraine.” Why is Ukraine involved?There is no evidence of any wrongdoing by Joe Biden or Hunter Biden. The allegations relate to Biden Jr’s time on the board of a Ukrainian energy company, Burisma, which was owned by a businessman who was being investigated by Ukraine’s top prosecutor.In 2016 the US and a number of other western countries pressured Ukraine to remove the prosecutor. Biden was vice-president at the time.Trump’s push for the Bidens to be investigated relates to the prosecutor’s removal. Trump’s assertions appear to be politically motivated. Joe Biden is favorite to win the Democratic nomination for president and polls show him beating Trump comfortably. Why is this so serious?It is illegal for a political campaign to accept a “thing of value” from a foreign government. Democrats say an investigation into a political opponent – for which Trump appears to have been pushing – would amount to a thing of value.It has also been suggested that Trump may have threatened to withhold military aid to Ukraine. About a month after the call, the US delayed $250m in such assistance. The money was released this month, after the existence of the whistleblower complaint became public.On Monday, at the United Nations in New York, Trump said of the call: “It’s very important to talk about corruption. If you don’t talk about corruption, why would you give money to a country that you think is corrupt? … It’s very important that on occasion you speak to somebody about corruption.”Trump also continued to seek to cast doubt on the whistleblower’s motivations, tweeting: “Who is this so-called ‘whistleblower’ who doesn’t know the correct facts. Is he on our Country’s side. Where does he come from?” Will the Trump-Zelenskiy transcript be released?Democrats and some Republicans have called for this to happen and it was reported on Monday that the White House is seriously considering doing so.Cabinet members Steven Mnuchin and Mike Pompeo, and White House press secretary Stephanie Grisham, have said releasing the transcript would set a damaging precedent, given the need for leaders to speak frankly in such calls.White House advisers are also reportedly worried that releasing the transcript would lead to calls for transcripts of conversations between Trump and other leaders – most notably Vladimir Putin – to be made public too. What are Democrats saying?On Monday Chuck Schumer, the Senate minority leader, wrote to the majority leader, Mitch McConnell, asking him to help obtain the whistleblower report and investigate why military aid was withheld. It seems unlikely McConnell will help him out.The House speaker, Nancy Pelosi, has said that if reports about the complaint bear out, Trump will face “serious repercussions” and the nation will have “grave, urgent concerns for our national security”.Pelosi has resisted pressure from the Democratic rank-and-file to impeach Trump over his links to Russia. The Ukraine revelations have only intensified calls for impeachment. On Sunday Adam Schiff, the Democratic chair of the House intelligence committee, told CNN “we may have crossed the Rubicon”.
