Special Counsel Robert Mueller is preparing to accelerate his probe into possible collusion between 
Donald Trump’s  presidential campaign and Russians who sought to interfere in the 2016  election, according to a person familiar with the investigation.
Mueller  and his team of prosecutors and investigators have an eye toward  producing conclusions -- and possible indictments -- related to  collusion by fall, said the person, who asked not to be identified.  He’ll be able to turn his full attention to the issue as he resolves  other questions, including deciding soon whether to find that Trump  sought to obstruct justice.
Mueller’s office declined to comment on his plans.
Suspicious contacts between at least 13 people associated  with Trump’s presidential campaign and Russians have fueled the debate  over collusion.
Some  of those encounters have been known for months: the Russian ambassador  whose conversations forced Attorney General Jeff Sessions to recuse  himself from overseeing the Russia investigation and led Michael Flynn  to plead guilty to perjury. The Russians who wangled a meeting with  Donald Trump Jr. at Trump Tower in July 2016 after dangling the promise  of political dirt on Democrat Hillary Clinton.
Other encounters continue to emerge, including a Russian’s chat with veteran Trump adviser Roger Stone at a cafe in Florida.
‘Warning Lights’
Signs  of suspicious Russian contacts first surfaced in late 2015, especially  among U.S. allies who were conducting surveillance against Russians,  according to a former official, who spoke on condition of anonymity.
                  
By the spring of 2016 the frequent contacts set off alarm  bells among U.S. intelligence officials, according to James Clapper, who  was director of national intelligence at the time. The FBI’s Russia  investigation officially began that July.
“The dashboard warning  lights were on for all of us because of the meetings,” Clapper said in  an interview this month. “We may not have known much about the content  of these meetings, but it was certainly very curious why so many  meetings with Russians.”
On three occasions, Russians offered  people associated with Trump’s campaign dirt on Democrat Clinton -- all  before it was publicly known that Russians had hacked the Democratic  National Committee and Clinton’s campaign chairman.
Mueller has  interviewed or sought information about many of the people known to have  met with Russians during the campaign. But it’s not known publicly  whether the barrage of Russian contacts was instigated or coordinated by  the Kremlin. Trump, for his part, has repeatedly denied any such  plotting, 
tweeting on June 15, “WITCH HUNT! There was no Russian Collusion.”
Here are the players and their known interactions, with links to previous news stories: > click link for full list