You may note that I called the investigation the "Trump/Russia Investigation" instead of the "Mueller Investigation". That's because I am tired of the news media calling it the Mueller Investigation. Robert Mueller is NOT being investigated. Donald Trump (and his underlings) and Russia are being investigated -- and the terminology should reflect that.
Trump's base and many of his GOP cohorts in Congress are now saying the Trump/Russia Investigation has gone on for too long. They would have you believe that because it has now passed the one-year mark, it should be stopped, because a year should have been enough time to discover anything that could be discovered.
They are hoping that not enough has been discovered to impeach or indict their favorite demagogue, and they want the investigation stopped before that can happen. I think they are wrong. I believe Mueller has uncovered a lot, and will continue his investigation until he feels he knows everything there is to know.
Is one year too long for a serious investigation to continue. No! let me direct your attention to the chart above (from fivethirtyeight.com). The Watergate (Nixon) investigation took over four years. The Iran-Contra (Reagan) investigation took over six years, and the Whitewater (Clinton) investigation took over seven years. Compared to these investigation, the Trump/Russia investigation is just in its infancy.
Note also that the Trump/Russia investigation has produced more indictments and pleas than any other investigation in its first year. The investigation needs to continue -- even (and especially) if it goes all the way to the president (as the Watergate investigation did).
Be patient. Mueller is doing his job.