“Stymied how?”
How about immigration and healthcare to start with — two of his basic promises? With the current House critters, and their liberal judges on secret retainer, he has been stymied in accomplishing those. And there are many, smaller, issues where they have stymied him.
The biggest promise of his that I’m dying to see is: “LOCK HER UP!”
And do you honestly believe that they wouldn't have done the same Mueller investigation or no Mueller investigation? McCain would still have detested Trump and done all he could to block his plans. The Democrats would still be in lock-step against him on immigration and healthcare because there is no willingness to work together on either side. Liberal judges would still be liberal judges. In the grand cosmic scheme of things the Mueller investigation changed nothing in terms of what Trump could have done and what he has done.