Trump lashes out at impeachment 'scam'

US President Donald Trump has labeled the current impeachment inquiry as the "greatest scam in the history of American politics," in a Twitter tirade late on Saturday.

"The Democrats want to take away your guns; they want to take away your health care; they want to take away your vote; they want to take away your freedom; they want to take away your judges; they want to take away everything," he said in a video post.

"Our country is at stake like never before," he warned.

He then retweeted more than 20 video posts from the Republican National Committee's opposition research team, which largely showed Republicans criticizing the earnestness of the impeachment process, downplaying the seriousness of the allegations and questioning the integrity of the anonymous whistleblower.

Trump defended his conversations with Ukrainian President Volodymyr Zelenskiy, saying the Democrat account of the call was fictitious.

The scattershot posts reveal some of the pressure that Trump and his administration are likely feeling as the Democrats push on with their impeachment inquiry into his alleged misuse of office and alleged attempted cover-ups.

Congressional committees have subpoenaed Secretary of State Mike Pompeo, compelling him to turn over Ukraine-related documents, investigating whether Trump jeopardized national security and the integrity of US elections.

Next week, they will interview five State Department officials, including former ambassador to Ukraine Marie Yovanovitch. Yovanovitch was reportedly fired for resisting Trump's efforts to pressure Kyiv to probe his Democratic rival Joe Biden.

Meanwhile, House Speaker Nancy Pelosi said Saturday public opinion now supports an impeachment inquiry.

"In the public, the tide has completely changed; it could change now — who knows — but right now after seeing the complaint and the inspector general report and the cavalier attitude the administration had towards it, the American people are coming to a different decision," Pelosi said at a journalism event hosted by the Texas Tribune news website.

"If the facts are persuasive to the American people, they may be to some Republicans," Pelosi said.

As revealed by an anonymous whistleblower earlier this month, and confirmed this past week by an official rough transcript released by the White House, during a July 25 telephone call, Trump asked Zelenskiy to investigate Biden and his son, Hunter, who had served on the board of a Ukrainian energy company. Both Bidens have denied any wrongdoing.