Donald Trump flew back to Washington on Thursday and into the biggest crisis of his tempestuous presidency, raging at enemies and talking darkly of a conspiracy.Trump's three day trip to New York was meant to showcase his achievements in a speech to the United Nations and multiple meetings with other world leaders.But everything vanished into the vortex of the Democrats' decision to open an impeachment investigation over allegations that he shook down Ukraine's president for dirt on Joe Biden, the current frontrunner to be his Democratic opponent in the 2020 presidential elections.The former real estate tycoon and reality TV performer returned to Washington on Air Force One as only the fourth president to face an impeachment inquiry.Trump goes further than merely insisting he did nothing wrong when talking to Ukrainian President Volodymyr Zelensky. Instead, he is painting the allegations as part of a plot, setting the stage for a political and legal struggle sure to stress an already divided country to its limits.Talking to reporters on the way back to the White House, Trump branded the Democrats a "disgrace".The impeachment procedures "shouldn't be allowed", he said."There should be a way of stopping it. Maybe legally, through the courts."Those comments were likely to spook opponents already claiming that Trump has repeatedly behaved - the Ukraine affair being only the latest example - as if he were above the law.About an hour earlier, The Los Angeles Times reported, Trump delivered even more unusual comments, telling US diplomats that the source of the whistleblower who first raised the alarm over the alleged Ukraine contacts should be treated as a traitor."You know what we used to do in the old days when we were smart? Right? The spies and treason, we used to handle it a little differently than we do now," he said according to the Times, which obtained a recording of the private event.View from the penthouseThe New York trip was meant to be quite different.The Big Apple is Trump's hometown and he returned like a modern-day emperor, traveling in a vast, heavily armed motorcade and staying in his own skyscraper, Trump Tower.Yet as the week progressed the view from that penthouse eyrie became grimmer. The man looking down became angrier.On Tuesday he boasted in front of the United Nations about what he called a historic peak in American military and economic might. However there were few diplomatic achievements to show.Iran remains a combustible, unsolved affair, with frantic efforts by French President Emmanuel Macron to facilitate a meeting between Trump and Iran's President Hassan Rouhani coming to naught.The China trade war rolls on. Attempts to force out Venezuela's leftist strongman Nicolas Maduro have failed. North Korea is not giving up nuclear weapons.That same afternoon, Democratic leader Nancy Pelosi announced the start of the formal impeachment probe, lighting a rocket under the already explosive 2020 presidential campaign.Few Americans had ever thought much about Ukraine, let alone its new president, Zelensky, who, like Trump, used to work in television entertainment.Suddenly the allegation that Trump twisted Zelensky's arm to prosecute a corruption case against Biden made Ukraine practically the only topic of discussion in Washington.As impeachment talk swelled, Trump agreed to release a transcript of a lengthy phone call he had with Zelensky. He then authorised the release of the complaint by the intelligence community whistleblower who'd raised the alarm in the first place.The White House said these documents killed the story."He has nothing to hide," spokesperson Stephanie Grisham said on Thursday.But for Democrats and even a few from Trump's ultra-loyal Republican party, the documents amounted to smoking guns.'All planned'The intensifying scandal turned Trump into an ever lonelier, downbeat figure.Usually his press conferences are stunning performances, filled with bragging, joking, storytelling and, above all, a willingness to take on any question.At times, Trump takes so many questions that journalists are visibly exhausted.On Wednesday, though, he ascended the podium to launch into a rambling monologue of over 20 minutes before taking just a few questions.It was a speech delivered in a flat voice, filled with an air of hurt."So many leaders came up to me today and they said, sir, what you go through, no president has ever gone through," he said.The man with answers to every question was stumbling, plunging into conspiracy theories that are echoed all over America on rightwing radio shows and websites."It was all planned," Trump said grimly. "That was all planned like everything else."