A second whistleblower has come forward, this one with first-hand information about events that triggered an impeachment investigation into President Donald Trump, the informant's lawyer said Sunday.

The original whistleblower alleged Trump abused his power as president by attempting to withhold US military aid to pressure his Ukrainian counterpart Volodymyr Zelensky into seeking damaging information on political rival Joe Biden.

As pressure mounted over the weekend, Trump pushed back in typical fashion Sunday and accused House Speaker Nancy Pelosi -- who announced impeachment proceedings last month -- of being guilty of "treason", and called for her to be impeached.

Earlier, the original informant's lawyer Mark Zaid, tweeted confirming an ABC News report that a second whistleblower was "represented by our legal team."

"They also made a protected disclosure under the law and cannot be retaliated against. This WBer has first-hand knowledge," he said.

Earlier, Zaid's co-counsel, Andrew Bakaj, said his firm and team "represent multiple whistleblowers" in the case.

However it was unclear whether Bakaj was using "multiple" to refer to more than two whistleblowers -- typically, several officials would listen in on a presidential call and a foreign leader.

The existence of a whistleblower claiming first-hand knowledge would make it harder for the president and his supporters to dismiss the original complaint as hearsay, as they have repeatedly done.

Trump pushes back

Trump pushed back at the allegations in tweets Sunday, but did not mention the second whistleblower.

He repeated his assertions that Joe Biden's son Hunter had been "handed $100,000 a month (Plus,Plus) from a Ukrainian based company, even though he had no experience in energy...and separately got 1.5 Billion Dollars from China despite no experience and for no apparent reason."

Hunter Biden was paid up to $50,000 a month as a board member for Ukrainian gas company Burisma, media reports said.

Trump tweeted that "as president I have an obligation to end CORRUPTION, even if that means requesting the help of a foreign country or countries. It is done all the time."

In a back-and-forth on Twitter, Biden responded: "In my experience, asking a foreign government to manufacture lies about your domestic political opponent is not 'done all the time.'"

US President Donald Trump, seen in this file photo on October 4, 2019 speaking to the press from the White House lawn, has called the impeachment inquiry a 'scam' by Democrats
US President Donald Trump, seen in this file photo on October 4, 2019 speaking to the press from the White House lawn, has called the impeachment inquiry a 'scam' by Democrats AFP / Andrew CABALLERO-REYNOLDS

Trump also said that Biden, among the leading Democratic presidential candidates for 2020, should "hang it up."

No evidence has been found that either Biden did anything illegal.

In perhaps his strongest response yet, Biden wrote in The Washington Post that Trump was "frantically pushing flat-out lies, debunked conspiracy theories and smears against me and my family, no doubt hoping to undermine my candidacy."

"It won't work, because the American people know me -- and they know him," Biden said in an op-ed article.

Trump remained in the White House on Sunday and -- despite the snowballing crisis -- no administration officials appeared on the morning television programs.

But Republican senator Ron Johnson told NBC that in conversation Trump had sharply rejected allegations he had linked military aid for Ukraine to any effort to find dirt on the Bidens.

"When I asked the president about that," said Johnson, who serves on the Foreign Relations Committee, "he completely adamantly, vehemently, angrily denied it."


Democratic-led House committees issued a series of subpoenas in the matter on Friday, including to the White House.

The impeachment saga began after the original whistleblower -- an intelligence official -- filed a formal complaint to the intelligence community inspector general about Trump's alleged pressuring of Zelensky.

A rough transcript of the phone call later released by the White House, as well as a series of text messages between US diplomats, appeared to corroborate the original complaint.

Democrats -- derided in a Trump tweet on Sunday as "DONOTHINGDEMOCRATS" -- insist they will continue pushing for action on key issues like health care and gun control, even as the impeachment inquiry absorbs a huge amount of Washington's attention and energy.

But in an appearance on NBC, former CIA director John Brennan raised questions about the country's continuing stability under Trump.

Asked how the CIA might assess the stability of the US -- as the agency does with other countries -- Brennan said: "We would look at it as a very corrupt government that is under the sway, right now, of this powerful individual who has been able to just corrupt the institutions and the laws of that country."

"I think there's a real question about the stability," he added.