President Trump resurrected one of his most brutal and repeated attacks from the 2016 campaign, blasting 'crooked' Hillary Clinton - less than 24 hours after it was revealed he is being investigated over obstruction of justice.

Trump slammed his former political rival in a series of tweets Thursday afternoon, after earlier terming a probe by a special counsel 'the single greatest WITCH HUNT in American political history - led by some very bad and conflicted people!'

Trump's complaint about 'obstruction' follows a bombshell Washington Post report that special counsel Robert Mueller was focusing on possible obstruction of justice related to the Russia investigation and Trump's firing of former FBI Director James Comey.

'Why is that Hillary Clintons family and Dems dealings with Russia are not looked at, but my non-dealings are?' Trump asked on Twitter.

President Donald Trump went after 'crooked' Hillary Clinton on Twitter, resurrecting attacks on his 2016 rival just hours after issuing a call for political unity

'Crooked H destroyed phones w/ hammer, 'bleached' emails, & had husband meet w/AG days before she was cleared- & they talk about obstruction?' Trump asked, combining his attacks on Clinton with gripes about the evolving Russia investigation.

The tweet revived two attacks from the 2016 campaign, that a Clinton aide destroyed some of her multiple communications devices, and that her team used software to get rid of old emails.

It also accuses, without evidence, Clinton of directing her husband Bill Clinton to hold his infamous Phoenix airport tarmac meeting with then-attorney general Loretta Lynch.

At the time it occurred, Clinton's campaign was not happy that the former president caused a major headache what was apparently an impromptu chat when Bill Clinton learned from agents that Lynch would be on the tarmac at the same time as him.

However Lynch's own actions are now under official scrutiny by the Senate Judiciary Committee after Comey revealed she had ordered the FBI to call its Clinton email probe 'a matter', not an investigation.

Trump's tweet followed a flurry of attacks and complaints.

Trump had told Americans Wednesday in a national address that the country is 'strongest when we are unified and when we work together for the common good' and asked them to remember that everyone in the nation's capitol is there out of love of country.

President Trump called Hillary Clinton 'Crooked H' again, as he fought back against the Washington Post report that the special counsel was looking into whether he tried to obstruct justice

WHEN YOU TALK ABOUT OBSTRUCTION: President Trump revived campaign attacks on Hillary Clinton, then asked: 'they talk about obstruction?'

His attack on his defeated rival – who has pointed to Russia, Comey, and a variety of factors for her defeat – comes less than a day after Trump issued a call for unity following the shooting of Rep. Steve Scalise (R-La.).

'We may have our differences, but we do well in times like these to remember that everyone who serves in our nation's capital is here because above all they love our country,' Trump said Wednesday at the White House.

'We can all agree that we are blessed to be Americans. That our children deserve to grow up in a nation of safety and peace. That we are strongest when we are unified and when we work together for the common good.'

In another tweet Thursday morning, Trump called the investigation into possible Russian collusion a 'witch hunt' led by 'bad people.'

Trump's attack that Clinton 'bleached' her emails was a reference to her use of BleachBit, an open source software to delete emails she considered private. His mention of her destroying phones was a reference to information, gleaned FBI documents released in September, than an aide destroyed two Clinton mobile phones that were no longer being used with a hammer.

SEEMS LIKE OLD TIMES: Donald Trump, 2016 Republican presidential nominee, speaks during the third U.S. presidential debate in Las Vegas, Nevada, U.S., on Wednesday, Oct. 19, 2016

Democratic Presidential Candidate Hillary Clinton celebrates her nomination following the completion of the DNC on July 28, 2016 in Philadelphia. President Trump resurrected his 2016 attack on her online Thursday

Trump went after Clinton for her email practices during the second presidential debate in October – where he also said he would appoint a special prosecutor to investigate her.

'The thing that you should be apologizing for are the 33,000 e-mails that you deleted and that you acid washed,' Trump said. 'You delete 33,000 e-mails. And then you acid wash them, or bleach them, as you would say—a very expensive process,'Trump said.

President Trump attacked his 2016 rival a day after it was reported that special counsel Robert Mueller's probe was looking at possible obstruction of justice

Sen. Charles Grassley, chair of the Senate Judiciary Committee, announced Thursday his panel would probe both possible obstruction of justice and Lynch's meeting with Bill Clinton.

Trump's White House contended Thursday afternoon that Trump did not fire the first shots and is not responsible for the return of gutter politics.

'I think there's been quite a bit of attacking against the president. I think he was responding to those specific accusations,' spokeswoman Sarah Huckabee Sanders told a reporter who asked about Trump's tone.

Huckabee Sanders said Trump had apparently taken steps on Wednesday to encourage more respectful behavior and is using his agenda to bring about unity.

The Republican president has taken many steps to reach out to Democrats, she said, and will continue to reach across the aisle.

Trump's spokeswoman rebuffed a reporter who asked about charges from legislators that he bears some responsibility for the hyper partisan atmosphere in the nation's Capitol that has reverberated across America.

'I think the president was extremely clear yesterday where he thought the rhetoric should lie. I'm not sure how you would say that he should own responsibility,' she replied.

Confronted with Trump's comments this morning in his tweets, Huckabee Sanders said, it was incumbent on the entire nation to bring down heat in political debates - and not just the president.

'I think as a whole our country certainly could bring the temperature down a little bit. I think that was the goal that the president laid out yesterday,' he said.

The White House spokeswoman went on to argue that Trump was doing just that with an agenda that 'helps empower all of America.'

Trump lashed out at The Washington Post on Thursday, after the storied newspaper claimed Justice Department special counsel Robert Mueller has widened his Russia probe to examine whether the president attempted to obstruct justice.

President Donald Trump lashed out on Thursday against a 'phony' Washington Post story and the 'witch hunt' that he says is fueling it

This new tentacle of the year-long FBI investigation, now being handled by Mueller, unfolded days after FBI Director James Comey was fired by Trump on May 9, according to the Post.

But Trump is hearing none of it, claiming that journalists are creating fake news to up the ante on a fake investigation.

'They made up a phony collusion with the Russians story, found zero proof, so now they go for obstruction of justice on the phony story. Nice,' he wrote on Twitter.

'You are witnessing the single greatest WITCH HUNT in American political history - led by some very bad and conflicted people! #MAGA,' Trump added in a second tweet.

Special Counsel Robert Mueller (left) is reportedly looking into whether Trump (right) obstructed justice, as his Russia probe expands

Comey testified last Thursday that he believed he was axed as a way to trip-up the Russia probe saying, 'It's my judgment that I was fired because of the Russia investigation. I was fired, in some way, to change – or the endeavor was to change the way the Russia investigation was being conducted.'

Comey also said Trump had pushed him to stop looking into former National Security Advisor Michael Flynn.

'I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy. I hope you can let this go,' Trump said, according to Comey.

Now Mueller's team wants to talk to others who were reportedly pressured by Trump on the issue.

Five sources told the Post that Director of National Intelligence Daniel Coats, NSA Director Mike Rogers and his ex-deputy Richard Ledgett agreed to be interviewed by Mueller's investigators.

The sit-downs could come as early as this week, the Post said.

The interviews suggest that Mueller, an ex-FBI chief himself, sees the 'he said, he said,' currently going on between Comey and Trump to be a bigger deal than just that, one of the Post's sources said.

The NSA told the paper it will 'fully cooperate with the special counsel,' while the office of the Director of National Intelligence and Ledgett declined to comment.

'The FBI leak regarding the president is outrageous, inexcusable, and illegal,' a spokesman for Trump's personal attorney Marc Kasowitz said.

The statement didn't challenge the accuracy of the Post's report.

But former Speaker of the House Newt Gingrich, a pointed Trump defender, tweeted that Mueller 'is now clearly the tip of the deep state spear aimed at destroying or at a minimum undermining and crippling the Trump presidency.'

'Deep state' refers to some conservatives' belief that a group of malicious actors within the government itself is conspiring to work at cross purposes with its leader.

The FBI probe was originally supposed to examine Russian meddling during the 2016 election, but had already expanded to looking into whether there was coordination between the Russians and the Trump campaign.

Comey's public admission of the latter, on March 20 before the House Intelligence Committee, rattled Trump and he asked the then-FBI director to make it clear publicly that the president wasn't personally under investigation.

Comey refused.

Trump defender Newt Gingrich, a former Speaker of the House, said special counsel Mueller is part of a 'deep state' intent on damaging the president

Trump then went to Coats and Rogers, making the same request.

Officials told the Post that Mueller is interested in conversations that took place on March 22, when Coats was less than a week on the job.

Coats was at the White House attending a briefing when Trump asked him, and CIA Director Mike Pompeo, to hold back.

Coats told the Post's sources that the president had requested that he ask Comey to get the FBI to back off of the investigation into Trump's ex-National Security Advisor Michael Flynn.

A day or two later, Trump called Coats, and also Rogers, and asked them to say publicly that there was no coordination between Russia and the Trump campaign.

The Post previously reported these exchanges, including that Trump's request was doubly denied.

Ledgett's involvement is unclear, though the Post's sources say he penned an internal NSA memo documenting Trump's call with Rogers.

When speaking before Congress last week, Coats said he never felt 'pressured' when interacting with the president.

Rogers said he wasn't 'pressured' either.

'In the three-plus years that I have been the director of the National Security Agency, to the best of my recollection, I have never been directed to do anything I believed to be illegal, immoral, unethical or inappropriate,' he told members of the Senate Intelligence Committee last Wednesday.

Neither official would say whether Trump made the ask.

That's a question that Mueller's team can ask, and that Coats and Rogers likely can't escape from in the long run.

Even though the White House can invoke executive privilege, the Supreme Court ruled during Watergate that government officials can't use privilege if they're withholding evidence in a criminal prosecution.