Watched by millions on TV, the Democrats steered the impeachment hearings against President Donald Trump towards allegations that his actions endangered national security and that he effectively tried to bribe Ukraine.
After weeks of secret hearings in a sub-terranean chamber, the Democrats who control the House of Representatives, brought the hearings to the open on Wednesday taking testimony from two senior diplomats who defied Trump to appear before the Intelligence Committee conducting the impeachment investigation.
Earlier the focus had been on Trump seeking Ukrainian interference in US elections by asking them to investigate the son of former Vice President Joe Biden, who is seeking to challenge Trump in next year's election.
Speaking to reporters with visiting Turkish President Recep Tayyip Erdogan, Trump repeated his long-standing complaint that the hearings were a "witch hunt" and a "hoax" which he was too busy to watch.
Testifying at the hearings, William Taylor, the top diplomat in Ukraine, said that delaying nearly $400 million in military assistance to Ukraine in an attempt to force President Volodymyr Zelensky to investigate Biden and his son affected national interests.
The Democrat Committee Chair Adam Schiff who had raised the Russian threat - Moscow has annexed Crimean region from Ukraine and supported anti-regime activists, some of them armed - asked Taylor: "How does this affect our national security?"
He replied: "Security was so important for Ukraine, as well as our own national interests. To withhold that assistance for no good reason other than to help with a political campaign made no sense."
In his opening remarks, Schiff brought up the term bribery - an offence laid out in the Constitution as grounds for impeachment - to characterise Trump allegedly conditioning release of aid to a probe of the Bidens.
He asked: "If he sought to condition, coerce, extort or bribe an ally into conducting investigations to aid his re-election campaign, and did so by withholding official acts -- a White House meeting or hundreds of millions of dollars of needed military aid a" must we simply aget over it?"
Most of the hearing was a rehash of the leaked secret testimony but carried out dramatically for the cameras.
The one new revelation came from Taylor who that said that one of his staffers had overheard a conversation between Trump and Gordon Sondland, the ambassador to the European Union. The staffer heard Trump ask about "the investigations" and Sondland telling him that "the Ukrainians were ready to move forward".
Deputy Assistant Secretary of State George Kent turned the focus on Trump's personal lawyer Rudy Giuliani, who was the driving force behind the investigations into the Bidens.
He said that Giuliani was running a parallel "irregular" foreign policy set up in dealing with Ukraine.
"It became clear to me that Giuliani's efforts to gin up politically motivated investigations were now infecting US engagement with Ukraine," he said.
Giuliani rose to international attention while he was the mayor of New York during the 9/11 attack on the city by Al Qaeda terrorists. Earlier he had been a federal prosecutor who was nicknamed the 'Sheriff of Wall Street' for his dogged pursuit of wrongdoing in the financial and stock market sectors, a singular passion he brought to investigating the Ukraine affair.
Kent admitted that he was concerned about the business dealings of Biden's son, Hunter, which created "the possibility of the perception of a conflict of interest".
The impeachment process revolves around Hunter Biden being appointed to the board of Ukrainian gas company, Burisma, with a monthly payment of $50,000 even though he had no prior experience in energy business and had been removed from the navy for drug use.
The Republicans have alleged that a Ukrainian inquiry into Burisma was scuttled at the behest of the former vice president.
Questioned by the Republicans' lawyer, Steve Castor, about the Burisma affair, Kent said that there was strong assumption that a prosecutor had taken a bribe to end the probe and he would "love" to see an inquiry into it.
The impeachment hearing has taken on the air of a court case with the witnesses making a statement and leaders on the committee from both parties and their lawyers cross-examining them, with the Democrats acting like prosecutors and the Republicans as the defence lawyers.
The impeachment process is basically to frame a chargesheet against Trump, which, if approved by the House, would go to the Senate for a formal trial presided over by the Supreme Court Chief Justice.
While the impeachment will be voted by the Democrat-controlled House, the Republican-controlled Senate is unlikely to vote to convict and remove Trump from office.
But the Democrats hope the drama of witnesses testifying before a national TV audience will work to their favour in next year's election even though Trump won't be ousted.
Only three impeachment proceedings have taken place against US Presidents -- Andrew Johnson in 1868, Richard Nixon in 1974 and Bill Clinton in 1998. Johnson and Clinton were impeached but not convicted in the Senate trials, while Nixon resigned before the process was completed.
Devin Nunes, the ranking Republican on the Intelligence Committee criticised what he called the "politicised bureaucracy", a reference to the two diplomats testifying as well to others in the administration.
"The main performance, the Russia hoax, has ended, and you've been cast in the low-rent Ukrainian sequel," he said.
The Democrats were disappointed when a special counsel who probed the allegations that Trump's campaign colluded with Russians in the 2016 found there was no collusion.
The move to impeach started after a Central Intelligence Agency officer at the White House complained that he had heard from someone that Trump had made an improper request to Zelensky during a July phone call with him.
The Republicans want the officer to testify before the impeachment inquiry, but Nunes has turned down the request. The person's identity is officially being kept a secret, although some media have outed the person.
During Wednesday's hearing, the Republicans said that there was no impropriety by Trump because the military aid was given to Ukraine and it had not started a probe of the Bidens.
As for the delay in releasing the military aid, they said it was because of the level of corruption in Ukraine and Trump wanted to be sure the new administration was genuinely against corruption and released it as soon Vice President Mike Pence and other officials were convinced about Zelensky's commitment to end corruption.
Nunes said Trump was a strong supporter of Ukraine and "approved the supply of weapons to Ukraine, unlike the previous administration, which provided blankets as defense against invading Russians".
One of the military items the Ukrainians wanted was anti-tank missiles.
"I was pleased when the Trump administration provided Javelin anti-tank missiles and enacted stronger sanctions," Taylor admitted.
The public impeachment hearings will continue on Friday when former ambassador to Ukraine Marie Yovanovitch, who was removed from the post, is to testify.