What is the difference under the US Constitution between the abuse of power and the usurpation of power?

At one time the US Supreme Court closely viewed and made decisions that took a strict view of executive branch actions that bordered on this distinction. Currently this view has been almost unpredictable, depending on what Court is current. Nevertheless usurpation is generally less dangerous for two reasons. One is that it is less likely to happen and-or less likely to be repeated. And, when it does, it will not create a constitutional precedent. On the other hand, abuse of power, in the Court's view would be extremely dangerous. It would provide for the so-called "snowballing effect" and executive powers as practiced by a president would do irreparable harm to the republic. While this may seem to be interpretive, each situation could be examined in detail should there be any doubt.