Trump lawyer Rudy Giuliani has said that if Mueller wants to interview Trump, he'll have to do so before September 1, because the Trump camp doesn't want to be the one to unduly influence the elections. Mueller himself appears to lean towards prolonging the case, and that may well be with an eye on doing exactly that.
And there's something else as well: as soon as the investigation wraps up, Trump will demand a second special counsel, this time to scrutinize the role the 'other side' has played in the 2016 presidential election and its aftermath.
He's determined to get it, and he'll fire both Jeff Sessions and Rod Rosenstein if they try to stand in his way.
There have of course been tons of signs that it's going to happen, but we got two significant ones just the past few days.