Later, they reportedly helped to set up a June 9, 2016 meeting at Trump Tower with several of Trump's campaign officials and Natalia Veselnitskaya, a lawyer with close links to the Russian government.
The President has escalated his attacks on the Mueller probe in recent days, and his tweet on Wednesday comes on the second day of former Trump campaign chairman Paul Manafort's trial, the first case Mueller's team has taken before a jury.
"This is a bad situation and Attorney General Jeff Sessions should stop this Rigged Witch Hunt right now, before it continues to stain our country any further", he tweeted. He also called it a "a disgrace to USA".
Though Trump has questioned whether Russian Federation was involved in the 2016 election, national intelligence director Dan Coats said, "We continue to see a pervasive messaging campaign by Russian Federation to try to weaken and divide the United States".
"It's the president's opinion", she said.
Trump has denied collusion and obstruction, describing Mueller's investigation as a witch hunt.
Mueller has wanted to question Trump about that possible obstruction of justice, along with potential collusion between his campaign and the Kremlin, for months. Mueller's team has offered the White House format changes, perhaps willing to limit some questions asked of President Donald Trump or accept some answers in writing.
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Trump's lawyers have been negotiating over an interview with Mueller since the end of previous year.
Dowd, who resigned from the president's legal team in late March, has said that Mueller's team made clear they would consider subpoenaing the president if he refused to sit voluntarily for an interview.
But Manafort's involvement in the Trump campaign spanned six months, and he led efforts to secure the GOP nomination for Trump in 2016.
Giuliani's remarks come a day after he called for Mueller's probe to present evidence of collusion between the US and Russian Federation during the 2016 election, or to disband the investigation altogether. "What they are doing is something that is important and we support and I don't think any efforts to truncate that or somehow shut it down early is in the public's best interest".
But Mr Manafort is not accused of aiding Russia's alleged attempts to sway the 2016 presidential election Mr Trump's way, a focus of the Mueller investigation. It's a campaign moment that's cast a cloud over Donald Trump Jr. and Jared Kushner, and incited the ire of President Donald Trump himself.
In effect, he believes he can convince the investigators for the special counsel, Robert Mueller, of his belief that their own inquiry is a "witch-hunt". Though experts believe obstruction by tweet is possible, prosecutors have to prove beyond a reasonable doubt that a particular act got in the way of an investigation and that the person who did it meant to obstruct.
The tweet renewed Democratic complaints that Trump is wrongly challenging the independence of the special counsel. At one point, the two sides had agreed to an interview at the end of January and were discussing the logistics when one of Trump's lawyers at the time, John Dowd, called it off.