The five most serious charges in the whistleblower's complaint

President Trump's troubles grew deeper and darker on Thursday morning when a whistleblower complaint became public.

Trump is facing serious threat of impeachment over his dealings with Ukraine and its president Volodymyr Zelensky. Speaker Nancy Pelosi (D-Calif.), a reluctant convert to the impeachment cause, is now spearheading the effort.

Trump and his allies are fighting back over the allegations. The president insists the whole matter is a "hoax" and that he did nothing wrong. 

White House press secretary Stephanie Grisham, in a Thursday morning statement, dismissed the complaint as "nothing more than a collection of third-hand accounts of events and cobbled-together press clippings-all of which shows nothing improper."

But those statements won't quell the storm, at least for now.

Here are the most serious allegations.

The White House sought to hide details of Trump's phone call

The central episode in the controversy is Trump's July 25 phone call with Zelensky, in which he pressed the Ukrainian president to investigate unsubstantiated allegations against former Vice President Joe Biden and his son Hunter.

The big revelation in the whistleblower's complaint is the suggestion that the White House sought to hide the word-for-word transcript of the call. 

This move was allegedly motivated, at least in part, because those with knowledge of the call realized "they had witnessed the President abuse his office for personal gain."

The whistleblower goes on to allege that "senior White House officials had intervened to 'lock down' all records of the phone call."

This effort, the complainant alleges, took the form of removing the "electronic transcript" of the call from the computer system where such transcripts would usually be stored and transferring it to a separate, more secure and more restricted system.

The core allegation is clear: The White House engaged in a cover-up. 

As former President Nixon discovered, such an allegation can be as politically dangerous as any underlying offense.

Trump allies used leverage to get Ukraine to 'play ball'

Trump's defenders have insisted that no quid pro quo was offered to Zelensky.

The complaint alleges otherwise - though it suggests such an incentive was held out by people close to the president rather than by Trump himself. 

The whistleblower asserts that "multiple U.S. officials" had told him or her that a phone call or meeting between Trump and Zelensky "would depend on whether Zelenskyy showed willingness to 'play ball.' " 

The complaint twice uses that phrase, in the second instance referring to the fact that a planned May trip to Ukraine by Vice President Pence to attend Zelensky's inauguration was canceled after Trump "instructed" Pence not to go. Energy Secretary Rick Perry went instead.

Citing unnamed officials, the whistleblower says that at this point, it was "made clear" to Ukrainian officials that Trump did not want to meet Zelensky "until he saw how Zelenskyy 'chose to act' in office." 

While the whistleblower acknowledges that he or she does not know if this was connected with the broader question of "playing ball," it is a very tricky question for Trump - and Pence - to handle.

The White House has hidden the details of other phone calls

The whistleblower alleges that other transcripts involving Trump had been placed into a secure system, for political reasons rather than because of legitimate national security concerns.

The whistleblower says that those officials said it was "not the first time" that transcripts had been placed into a "codeword-level" system - and that this had been done "solely for the purpose of protecting politically sensitive - rather than national security sensitive - information."

The details here are entirely opaque. But it gives Democrats another thread to pull as impeachment inquiries continue.

Officials were 'deeply concerned' by Giuliani's activities

The president's personal lawyer, Rudy Giuliani, has acknowledged pressing Ukraine to investigate the Bidens. 

He has also given a series of media interviews in recent days, as controversy around his role intensifies. There has also been considerable back-and-forth as to whether Giuliani was acting with the imprimatur - or at least the consent - of figures at the State Department, or not.

The whistleblower complaint adds fuel to those fires inside the administration. It alleges that "multiple U.S. officials" were "deeply concerned by what they viewed as Mr. Giuliani's circumvention of national security decisionmaking processes to engage with Ukrainian officials and relay messages back and forth between Kyiv and the President."

Giuliani told CNN on Thursday morning that he had "no knowledge of any of that crap" in the complaint.

Ukrainian officials knew U.S. aid could be in jeopardy

No one disputes that about $400 million in aid that Congress had voted to supply to Ukraine was delayed by the administration. 

The question is whether that was linked, in an identifiable way, with Trump's desire for Ukraine to dig for dirt on the Bidens.

The whistleblower does not answer this question definitively. 

But the complaint affirms prior media reporting that Trump had at one point ordered the suspension of U.S. "security assistance" to Ukraine. 

The complaint notes two specific dates, July 23 and July 26, when officials from the Office of Management and Budget allegedly "stated explicitly that the instruction to suspend this assistance had come directly from the President, but they still were unaware of a policy rationale."

Importantly - at least from the standpoint of the degree of pressure brought to bear on Ukraine- the whistleblower said that in early August "U.S. officials" had told him or her "that some Ukrainian officials were aware that U.S. aid might be in jeopardy."

Trump has said the aid was delayed because he wanted other allies of Ukraine to commit to offering support.