WASHINGTON(Reuters) - U.S. President Donald Trump has maintained throughout the impeachment inquiry that he did nothing improper in his dealings with Ukraine, even as witnesses have detailed efforts by his White House to get Ukraine to take actions that could help him politically.

U.S. President Donald Trump speaks to reporters as he and first lady Melania Trump depart for travel to a NATO summit in London, from the White House in Washington, U.S. December 2, 2019. REUTERS/Jonathan Ernst

Here are Trump’s positions on the main aspects of the investigation:

JOE BIDEN, UKRAINE AND THE 2016 ELECTION

Trump says he did not ask Ukrainian President Volodymyr Zelenskiy to investigate Joe Biden, a leading contender for the Democratic nomination in the 2020 presidential election, for corruption. Instead, he said, he had been pressing for a broad anti-corruption crackdown in Ukraine.

“Are we going to be sending massive amounts of money to a country and they’re corrupt and they steal the money and that goes into everybody’s bank account?” Trump said on “Fox and Friends” on Nov. 22.

But a rough transcript of a July 25 telephone call shows that Trump asked the Ukrainian president to investigate whether Biden, while U.S. vice president, pressed Ukraine to fire Ukraine’s top prosecutor to stop a probe of Burisma, a gas company which Biden’s son Hunter had worked for as a director.

Biden and his son have denied any wrongdoing, and no evidence has emerged to substantiate the allegations.

Trump also asked Zelenskiy to look into a conspiracy theory that Ukraine, not Russia, interfered in the 2016 election and that an email server used by the Democratic Party is being hidden in the country.

“I would like you to find out what happened with this whole situation with Ukraine,” he said on the call. “The server, they say Ukraine has it.”

NO QUID PRO QUO

Trump says he did nothing wrong in his dealings with Zelenskiy and points to the impeachment inquiry testimony of Gordon Sondland, a Trump donor and U.S. ambassador to the European Union, who said the president told him in a phone call on Sept. 9 that he wanted no “quid pro quo” from Ukraine in return for the release of much-needed military aid.

Sondland testified, however, that the White House declined to invite Zelenskiy to meet with Trump in Washington in order to pressure the Ukrainian president to announce the investigations Trump wanted.

Sondland said that “everyone was in the loop” at the highest levels of the Trump administration about the pressure campaign.

Sondland said he gradually came to believe that the White House was holding back the $391 million in security aid to pressure Ukraine.

Trump’s acting chief of staff, Mick Mulvaney, acknowledged that White House withheld the money in order to push Ukraine to investigate the 2016 election, although he later reversed those comments.

Trump has acknowledged that he held up the military aid, saying he wanted to encourage the country to tackle corruption in a broad sense. Transparency International, a non-governmental organization, ranked Ukraine in the top third of the most corrupt countries in a global index.

Trump did not address corruption in his July call with Zelenskiy and he did not bring it up the first time the two men spoke shortly after Zelenskiy was elected in April, records from both calls show.

Trump ultimately released the money on Sept. 11, after news of the freeze became public.