The point of the Mueller investigation was to get Trump to testify in person so they could trap him in a manufactured obstruction of justice charge. (An annex to the Mueller report laid out Andrew Weisman's twisted view of the obstruction of justice statute. They hoped to make this charge stick.)

The goal of a second special counsel will be the same. If Trump does not cooperate with the investigation, they will charge him with obstruction of justice and let the chips fall where they may.