There's a new political controversy in the US – involving Donald Trump, foreign nationals, questions about legal and ethical behaviour, and allegations against a political rival.
This feels a bit like déjà vu from 2016, with Russia, then-candidate Trump and Hillary Clinton, but it's a new country (Ukraine) and a new cast of characters (Joe Biden and his son Hunter).
Mr Trump is still right smack in the middle, of course.
The story can be difficult to follow, so here are some answers to the most pressing questions.
Why is this important?
Mr Trump's most ardent critics accuse him of using the powers of the presidency to bully Ukraine into digging up damaging information on a political rival, Democrat Joe Biden.
Meanwhile, Mr Trump and his supporters allege the former vice-president abused his power to pressure Ukraine to back away from a criminal investigation that could implicate his son, Hunter.
Mr Biden is the front-runner for the Democratic nomination to take on Mr Trump next year.
In other words, it is nothing less than the White House at stake.
Where does this row stem from?
According to multiple media reports, Mr Trump and Ukraine President Volodymyr Zelensky had a phone conversation on 25 July this year.
The US president is alleged to have pressed his Ukrainian counterpart to investigate former Vice-President Biden.
Mr Trump may have also discussed the $250m (£201m) in military aid Congress approved for Ukraine – aid that the Trump administration had delayed releasing until mid-September.
The Washington Post and other US media say Mr Trump told his acting chief of staff, Mick Mulvaney, to hold back the aid at least a week before the phone call.
Has Mr Trump confirmed any of this?
Mr Trump said that he spoke to Mr Zelensky about the problem of corruption and also about Mr Biden and son Hunter among other issues.
It was a "nice conversation" on the phone – a "perfect" call.
The US gives aid to Ukraine so "we want to make sure that country is honest," he added.
On Twitter, Mr Trump has been more blunt, saying the controversy was created by Democrats and the "Crooked Media".
He has also tacitly questioned the "supposed" whistleblower's patriotism.
What are other US politicians saying?
Congressional Democrats say the phone call – raised by a whistleblower in a formal complaint – is important because it helps to shed light on the president's dealings with the foreign leader.
Critics of the White House say that Mr Trump put pressure on Mr Zelensky, urging him to tell officials in his government to investigate business activities related to Hunter Biden, who was a board member for a company owned by a Ukrainian oligarch.
Democrats said that the president wanted the Ukrainians to start the investigation into corruption because this could sully the reputation of Hunter and his father.
Republicans have said little about the controversy. This shows the partisan nature of the controversy, which has – like much else in Washington – been divided by party politics.
However, at least one Republican, Mitt Romney, a US senator from Utah, said he would like to know more.
What happened to the whistleblower's complaint?
After receiving the complaint, the inspector general informed Joseph Maguire, the acting director of national intelligence, and said the matter was "urgent". The intelligence community whistleblower law says the director has seven days to pass the complaint along to congressional intelligence committees.
That didn't happen.
Instead, Mr Maguire spoke to a lawyer who told him the issue was not "urgent", at least according to legal standards, according to the New York Times.
As a result, Mr Maguire decided that the members of the congressional oversight committees did not need to see it.
On 9 September, the inspector general informed Congress about the complaint's existence, but not the details. Democrats in Congress have since clamoured for more information – including a transcript of Mr Trump's call – but the administration has refused to co-operate.
And that's where things currently stand.
Mr Maguire is scheduled to testify publicly before the House Intelligence Committee on Thursday, and lawmakers are likely to say they want to see the complaint. If that does not work, House Intelligence Committee Chair Adam Schiff might file a lawsuit, according to CNN, to try to get access to it.
So did the president do something illegal?
The most damning allegation is that the president pressured a foreign leader for damaging information about a political opponent while holding out the prospect of US military aid.
Is that illegal? We do have some very recent precedent.
It certainly recalls the recently concluded two-year Robert Mueller investigation into possible Trump campaign ties to Russian election-meddling in 2016.
The special counsel's report detailed multiple contacts between the campaign and Russian nationals, including the June 2016 meeting between top campaign officials such as Donald Trump Jr and several Russians with ties to the Kremlin.
There has been some debate over whether soliciting opposition research from a foreign government constitutes a campaign finance violation, but Mr Mueller declined to file charges.
Mr Trump's Ukrainian call could also potentially run afoul of federal bribery statutes. The special counsel concluded that Justice Department policy guidelines prohibit a sitting president from being indicted, however, so even if Mr Trump did commit some kind of crime with his actions, he's safe at the moment from criminal prosecution.
With this in mind, a more relevant question might be …
Did Mr Trump commit an impeachable offence?
The constitutional process for handling a president who committed illegal and-or unethical acts is impeachment by a majority of the House of Representatives and conviction and removal by a two-thirds majority of the US Senate.
The US constitution outlines the grounds for impeachment as "treason, bribery, or other high crimes and misdemeanors". When it comes down to it, an "impeachable offense" is whatever a majority of the House says it is.
Ever since the conclusion of the Mueller investigation, the drumbeat for impeachment among Democrats – who hold a comfortable majority in the House – has been steadily increasing. Up to now, however, the House Democratic leadership has been loath to push ahead with a formal investigation that could lead to an impeachment vote.
Speaker of the House Nancy Pelosi has suggested that suRead More – Source