Second Whistleblower In Trump-Ukraine Scandal With 'First-Hand Knowledge' Comes Forward

A second whistleblower has emerged with information that backs the original whistleblower's complaint about President Donald Trump's dealings with Ukraine, according to a lawyer for both sources.

The second whistleblower, who also works in intelligence, has spoken to the intelligence community's internal watchdog.

His lawyer Mark Zaid said he hasn't filed a complaint with the inspector general but does have "firsthand knowledge" that supported the original whistleblower, a CIA officer.

The original whistleblower filed a formal complaint with the inspector general on August 12 that triggered the impeachment inquiry being led by Democrats in the US House of Representatives.

President Donald Trump has repeatedly stated it's his "right" to have foreign governments investigate US nationals. Photo: AAP.

The complaint alleged Trump was "using the power of his office to solicit interference from a foreign country" in the 2020 election.

Trump and his supporters have rejected accusations he did anything improper.

But the White House has struggled to come up with a unified response. No administration officials appeared on the Sunday news shows, but several congressional Republicans came to the president's defence during television interviews.

Republican Jim Jordan of Ohio and Senator Lindsey Graham of South Carolina, two of Trump's most vocal backers, sharply criticised the way House Democrats are handling the impeachment inquiry.

Graham said there was nothing wrong with Trump's July phone call during which the president pressed Ukrainian President Volodymyr Zelenskiy to investigate former vice president Joe Biden and his son, Hunter.

The conversation has raised questions about whether Trump was using nearly $US400 million ($A591 million) in critical American military aid to Ukraine as leverage to get help on the Biden issue.

Joe Biden is a leading candidate for the 2020 Democratic presidential nomination.

"I think this is a nightmare for the Biden campaign," Graham said.

Democratic presidential candidate, former Vice President Joe Biden speaks at the New Hampshire Democratic Party Convention at the SNHU Arena on September 7, 2019 in Manchester, New Hampshire. Photo: AAP.

Biden wrote in The Washington Post that he had a message for Trump and "those who facilitate his abuses of power".

"Please know that I'm not going anywhere. You won't destroy me, and you won't destroy my family," Biden wrote.

Rather than visiting his nearby golf course in Sterling, Virginia, for a second day, Trump stayed at the White House and tweeted and retweeted, with the Bidens a main target.

"The great Scam is being revealed!" Trump wrote at one point, continuing to paint himself as the victim of a "deep state" and hostile Democrats.

Trump trumpeted his strong support among Republican voters and again lashed out at Utah Senator Mitt Romney, one of the few Republicans who has publicly questioned Trump's conduct.

"The Democrats are lucky that they don't have any Mitt Romney types," Trump wrote, painting the former Republican nominee as a traitor to his party.

A protesters, right, holding a banner blows a whistle as the motorcade of President Donald Trump arrives at the Trump National Golf Club in Sterling, Va., Saturday, Oct. 5, 2019. Photo: AAP.

Florida Democrat Val Demings said she believes the original whistleblower is a "patriot" who stepped forward to report wrongdoing despite the potential career risk.

"The reporting that a second whistleblower has come forward or is about to come forward, I believe again would be someone who sees wrongdoing, hears wrongdoing and wants to do something about it," Demings said.