WASHINGTON – Amid what could be a mortal threat to his presidency, Donald Trump spent Friday attacking a key impeachment investigator and the whistleblower whose complaint triggered the latest impeachment drive.

"Sounding more and more like the so-called Whistleblower isn’t a Whistleblower at all," Trump tweeted during what looked like a preview of his impeachment communications strategy seeking to undermine his accusers.

"In addition," Trump said, "all second hand information that proved to be so inaccurate that there may not have even been somebody else, a leaker or spy, feeding it to him or her? A partisan operative?"

Lawmakers – including Rep. Adam Schiff, D-Ca., the House Intelligence Committee chairman also under attack by Trump – said the whistleblower's complaint is backed by evidence that Trump tried to pressure the president of Ukraine into investigating political rival Joe Biden.

"You engaged in a shakedown to get election dirt from a foreign country," Schiff to Trump of Twitter. "And then you tried to cover it up. But you’re right about one thing – your words need no mockery. Your own words and deeds mock themselves. But most importantly here, they endanger our country."

Schiff was responding to Trump's tweeted complaint that Schiff misrepresented his conversation with Ukraine's president Volodymyr Zelensky, one in which Trump talked about foreign aid in connection with a request to have Ukraine investigate Biden.

"Adam Schiff therefore lied to Congress and attempted to defraud the American Public," Trump said. "He has been doing this for two years. I am calling for him to immediately resign from Congress based on this fraud!"

Schiff responded that Trump is the liar. He tweeted back at Trump that the House will continue to investigate claims that he tried to enlist a foreign government to help his 2020 campaign by smearing a Democrat rival.

The two politicians, who have fought previously over the Russia investigation, renewed their battle a day after the release of a whistleblower's complaint that Trump improperly pressured Zelensky.

The whistleblower is still unnamed.

In statements and emails throughout the week, Trump and allies argued that the whistleblower's complaint doesn't go much beyond what wasn't already known.

The report, however, alleged Ukraine officials were aware that Trump wanted to discuss the issue before the July 25 call at the center of the controversy and said aides tried to "lock down" notes from Trump's call to Ukraine.

It also provides more details of Trump's interactions with the Ukrainian leader. The whistleblower suggests that Trump and aides tried to cover up his push for a foreign country to investigate a rival before the 2020 election by storing the notes of the call in a separate computer system reserved for highly sensitive material.

The whistleblower said some administration officials expressed concern that Trump "used the power of his office" to benefit himself and his reelection campaign.

Trump also tweeted out a campaign video that spotlighted his accusations against Biden and claimed the Democrats are seeking to use impeachment as an election issue.

"They lost the (2016) election," the narrator of the ad says. "Now they want to steal this one. Don't let them."

More:Former Ukrainian prosecutor: I'm not aware of 'any possible violation of Ukrainian law' by the Bidens