WASHINGTON (NYTIMES) - The United States House of Representatives held its inaugural open impeachment hearing on Wednesday (Nov 13), taking public testimony for the first time since endorsing the formal inquiry into allegations against President Donald Trump.

Mr William Taylor Jr, the top US diplomat in Ukraine, and Mr George P. Kent, a senior State Department official in charge of Ukraine policy, both testified about Mr Trump's campaign to pressure Ukraine to investigate former vice-president Joe Biden, one of his leading political rivals.

Here are some of the key takeaways from Wednesday's hearing.

1. A STUNNING NEW DETAIL

Mr Taylor testified that a member of his staff overheard a telephone conversation in which Mr Trump pressed Mr Gordon Sondland, the US ambassador to the European Union, on "the investigations". Afterwards, when the aide asked Mr Sondland about the President's thoughts on Ukraine, Mr Sondland said Mr Trump cared more about "investigations of Biden".

The new detail, which Mr Taylor recounted for the first time on Wednesday after having learnt of it only recently, brought to life the core of Democrats' argument in the impeachment inquiry. It suggested that the President's obsession with discrediting his political rivals led him to put his own interests ahead of the nation's in his dealings with Ukraine.

It was the biggest revelation in more than five hours of testimony that largely matched what had been said behind closed doors.

2. CAREER OFFICIALS STRUGGLED

Mr Kent told lawmakers that efforts by Mr Rudy Giuliani, the President's personal lawyer, to pressure President Volodymyr Zelensky of Ukraine to open investigations into Mr Trump's political rivals "were now infecting US engagement with Ukraine, leveraging President Zelensky's desire for a White House meeting".

Ultimately, Republicans argued, nearly US$400 million (S$545 million) in military aid was delivered to Ukraine. But both Mr Kent and Mr Taylor detailed how that process was muddled by efforts within the administration to push Mr Zelensky to publicly announce investigations that could benefit Mr Trump in his campaign for re-election.

3. REPUBLICANS SHOWED THEIR PLAN

Republicans, through their top lawyer and their own questioning, offered a glimpse of how they plan to counter the damning accounts from administration officials: by painting them as bureaucrats with an agenda but no first-hand knowledge of the president's actions.

Both witnesses took care to outline their apolitical backgrounds, noting that they had served under Republican and Democratic presidents.

But Representative Devin Nunes of California, the top Republican on the Intelligence Committee, said they were part of a "politicised bureaucracy", where State Department officials worked to undermine an unconventional president and his foreign policies.

4. DEMOCRATS SHOWED THEY HAVE LEARNT

The hearing was the opposite of the ones Democrats convened to hear from Mr Robert Mueller, the special counsel who investigated Russian interference in the 2016 election, and Mr Corey Lewandowski, a former aide to Mr Trump. That was by design.

Lawmakers ceded the opening hours of testimony to their counsels, allowing trained lawyers from each side to pursue substantive lines of questioning in lengthy rounds, instead of the usual rapid-fire, five-minute bursts from lawmakers, who often use their time to make political points.

Representative Adam B. Schiff of California, the chairman of the Intelligence Committee, also maintained a controlled environment, preventing most interjections from Republicans and quickly dispensing with their efforts to hear more from the whistle-blower who first raised concerns about the President's conduct.

Lawmakers also had a much more willing pair of witnesses on Wednesday, when Mr Taylor and Mr Kent came ready to answer detailed questions and did not shy away from providing their opinions and observations.

5. LAWMAKERS' OPINIONS DIDN'T BUDGE

The initial House vote to lay out rules for the inquiry was starkly partisan, splitting along party lines with just the exception of two Democrats joining Republicans in voting against the measure. And despite the new revelation on Wednesday, not one lawmaker appeared to shift positions on the idea of impeaching Mr Trump.

Members of both parties emerged from the hearing saying it had helped their side's arguments.

Representative Jim Jordan, a Republican from Ohio, who joined the Intelligence Committee for the impeachment inquiry, declared it "a good day for the facts, and a good day for the president of the United States".

Minutes later, Mr Schiff told reporters that the witnesses had painted a picture of a rogue foreign policy channel within the administration in which Mr Trump "sought to advance his political and personal interest at the expense of the United States' national security".