"The 13 Angry Democrats (plus people who worked 8 years for Obama) working on the rigged Russia Witch Hunt, will be MEDDLING with the midterm elections, especially now that Republicans (stay tough!) are taking the lead in Polls," Trump wrote on Twitter, adding: "There was no Collusion, except by the Democrats!"
The probe, which recently marked its first anniversary, is headed by Mueller, a longtime Republican, and overseen by Deputy Attorney-General Rod Rosenstein, a Republican and a Trump appointee.
But publicly available voter-registration information shows that 13 of the 17 members of Mueller's team have previously registered as Democrats, while four had no affiliation or their affiliation could not be found. Justice Department policies prohibit discrimination in hiring for career positions on the basis of politics.
In a second tweet, Trump said the Special Counsel's team should instead be investigating the campaign of his Democratic opponent in the 2016 election, whom he described as "totally Crooked Hillary Clinton."
"Why aren't the 13 Angry and heavily conflicted Democrats investigating the totally Crooked Campaign of totally Crooked Hillary Clinton," Trump wrote. "It's a Rigged Witch Hunt, that's why! Ask them if they enjoyed her after election celebration!"
During his campaign against Clinton, Trump claimed that she should have been prosecuted harshly for lax security in her government email practices when she was Secretary of State. His campaign rallies frequently began with chants of "lock her up."
Trump is now claiming that the FBI went easy on Clinton and that some people involved in making that decision are working against him in the Mueller probe.
When polls suggested that he would lose to Clinton in 2016, Trump cast doubt on the validity of the election process and said at one point that he might not respect the outcome unless he won.
In another tweet, Trump suggested that the Russia probe was taking away some of his focus on other issues confronting the country, including trade deals and the effort to denuclearise North Korea.
"Sorry, I've got to start focusing my energy on North Korea Nuclear, bad Trade Deals, VA Choice, the Economy, rebuilding the Military, and so much more, and not on the Rigged Russia Witch Hunt that should be investigating Clinton/Russia/FBI/Justice/Obama/Comey/Lynch etc." the President wrote.
Trump has at some point attacked each person or organisation on his slash-marked list. In the case of the FBI and Justice Department, that has meant assailing the credibility of elements of the federal government that are part of the Mueller effort.
US intelligence agencies have said they have high confidence that Russia attempted to interfere in the 2016 election to hurt Clinton. By default, that effort would have helped Trump, but Mueller is looking into whether Trump associates played a more an active role.
Trump's former campaign manager, Paul Manafort, is among 19 individuals and entities indicted by Mueller. Some of Mueller's actions remain under seal.
Russia denies it interfered in the election.
Among those pushing back against Trump's assertions was Senate Minority Leader Chuck Schumer, (D), who noted the growing list of indictments and guilty pleas in the Mueller probe.
"Mueller's work is that of a career prosecutor and law enforcement officer who is squarely focused on getting to bottom of Russia's meddling in our elections and any possible collusion with your campaign and a hostile foreign government," Schumer wrote in a tweet directed at Trump.
Trump's lawyer, Rudy Giuliani, said that the President is attacking the Mueller probe because the tactic is working.
"As an effective politician, you're not going to do something that you don't think is working," Giuliani said.
