President Donald Trump on Sunday assailed Democrats' effort to have special counsel Robert Mueller testify before Congress about his report on the "sweeping and systematic" interference by Russia in the 2016 election.

On Twitter, Trump slammed the move as an attempt at a "redo" of the investigation, which did not find any evidence of a criminal conspiracy or any coordination between the Trump campaign and the Russian government.

He wondered why, after "spending more than $35,000,000 over a two year period, interviewing 500 people, using 18 Trump Hating Angry Democrats & 49 FBI Agents - all culminating in a more than 400 page Report showing NO COLLUSION," the Democrats in Congress now need Robert Mueller to testify."

"There was no crime, except on the other side (incredibly not covered in the Report), and NO OBSTRUCTION. Bob Mueller should not testify. No redos for the Dems!"

Trump's opposition to Mueller's testimony contrasted with his response last week in the Oval Office what he thought about the possibility.

"I don't know. That's up to our attorney general, who I think has done a fantastic job," Trump said Friday.

House Judiciary Committee member Rep. David Cicilline on Sunday walked back a claim that special counsel Robert Mueller had agreed via a representative to testify on May 15 about his report on the Russian government's efforts to interfere in the 2016 election.

"We hope the special counsel will appear," he said in a "Fox News Sunday" interview. "We think the American people have a right to hear directly from him."

"Just to clarify: we are aiming to bring Mueller in on the 15th, but nothing has been agreed to yet. That’s the date the Committee has proposed, and we hope the Special Counsel will agree to it. Sorry for the confusion," the Rhode Island Democrat said in a tweet later that day.

House Judiciary Committee Chairman Jerry Nadler, D-N.Y., said last week that he hoped to have Mueller testify on May 15.

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Just to clarify: we are aiming to bring Mueller in on the 15th, but nothing has been agreed to yet. That’s the date the Committee has proposed, and we hope the Special Counsel will agree to it. Sorry for the confusion. https://t.co/FfR8ReLmkp — David Cicilline (@davidcicilline) May 5, 2019

Congressional Democrats have expressed concern about Attorney General William Barr's handling of Mueller's 448-page report. They objected to his summary of its principal conclusions and Barr's decision not to charge President Donald Trump with obstruction of justice, and want to ask Mueller about his opinion on those matters.

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After spending more than $35,000,000 over a two year period, interviewing 500 people, using 18 Trump Hating Angry Democrats & 49 FBI Agents - all culminating in a more than 400 page Report showing NO COLLUSION - why would the Democrats in Congress now need Robert Mueller....... — Donald J. Trump (@realDonaldTrump) May 5, 2019

....to testify. Are they looking for a redo because they hated seeing the strong NO COLLUSION conclusion? There was no crime, except on the other side (incredibly not covered in the Report), and NO OBSTRUCTION. Bob Mueller should not testify. No redos for the Dems! — Donald J. Trump (@realDonaldTrump) May 5, 2019

The president has often repeated the claim that it was "the other side" that acted illegally in 2016, although he does not specify what crimes were committed or by whom.

The president is likely referring to the counterintelligence investigation that was launched against his campaign, and which he has derided as "spying." On several occasions, he has said the origin of the investigation constitutes a scandal "bigger than Watergate."

Barr has indicated he plans to investigate the president's concerns about how the investigation began into possible links between the Trump campaign and the Kremlin.

Cicilline said Sunday that the origins were of the investigation were "laid out in the Mueller report in pretty significant details."

"More than 140 contacts between the Trump campaign and Russian officials or people connected to WikiLeaks. We know how the investigation began. What we ought to be focusing on is protecting America from an attack by a foreign adversary of our democracy," he said.

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Despite Trump's objections on Twitter, Cicilline said the "White House has so far indicated they would not interfere with Mr. Mueller’s attempts to testify."

"We hope that won't change."

Barr skipped a scheduled hearing last week where he was to testify before the House Judiciary Committee about the Mueller report. Nadler said Barr had objected to being questioned by lawyers hired by the committee and to the possibility of extended questioning behind closed doors.

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Cicilline asserted that "Congress has the absolute responsibility to collect evidence and to compel the presence of witnesses to testify under oath. If the executive branch can prevent us from doing that, they will have effectively extinguished our oversight function. So, we have to take this in a deadly serious way."

He said Congress could enforce a subpoena against Barr by initiating a civil proceeding to hold him in contempt. Or, he said, the Supreme Court supported Congress' in 1821 and 1935 when "individuals were taken into custody pending their compliance with the subpoena."

But Cicilline said "of course" it "should never come to that."

"We expect the attorney general to honor a subpoena when properly served, and we will fully enforce that through the courts. But the reality is, we have to have access to this information," he said.

"This is central to our oversight responsibilities, and it is not up to the executive branch to decide what they want to give us. Our Constitution requires otherwise."

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This article originally appeared on USA TODAY: Trump now slams Democrats' efforts to have Mueller testify as attempt at report 'redo'