The Crucible is peculiarly subtle in the way it depicts the complexity of power, so that different characters wield different types of power throughout the play. As the action begins, John Proctor is not a particularly powerful man—certainly not when compared with a high-level official such as Danforth, a wealthy magnate like Putnam, or even a figure of spiritual authority like Hale. What he does have, however, is control over his own life and destiny. This is admittedly compromised by the chill in his relations with Elizabeth, but even in this area, Proctor asserts himself in act 2 and is able to maintain a high degree of control over his own circumstances.
In acts 3 and 4, Proctor's control over his own life recedes, even as his voice in the public sphere grows more powerful. By the end of the play, he has become a powerful figure of integrity and dissent, potent enough to frighten Danforth and drive Hale to despair. At the same time, he has lost control of his personal circumstances to the extent that he no longer has the power to save his own life, let alone determine the course of it. The effect of this is mitigated to some extent by the atmosphere in act 4, when Salem is in chaos and no one seems to have any power or control. In this sense, Proctor's loss of control over his own life is symbolic of what is happening to everyone.
It's ironic indeed that as John Proctor starts to find his voice and stand up for the truth, he becomes less and less powerful. Before the Salem witch-craze took hold, it was the other way round. John was lord and master in his own little domain, exercising the dominant role as head of the house. He also exercised a fair degree of power in conducting his illicit extramarital affair with Abigail Williams.
But when his wife, Elizabeth, finds out about the affair and fires Abigail from her job as a housekeeper, it's noticeable that John's control over events starts to wane. From now on, he finds that he's responding to events rather than shaping them. The power dynamic at the heart of his relationship with Abbie has undergone a complete reversal. Now she's the one who's in control, making false accusations of witchcraft left, right, and center and holding the power of life and death over the townsfolk of Salem, including John Proctor.
Eventually, John stands up to the prevailing madness, but it's all too late. For all his incredible bravery, he still lacks the power to shape events; his fate is in other people's hands now. All he can do is hope that posterity will look kindly on the Proctor family name.
During the period that is covered by the play, John Proctor’s power within his community fluctuates until it he loses all of it. The seeds of this loss began long before the point where the first act begins, however. Proctor’s road toward the total loss of power began with his sin—in the eyes of his fellow Puritans—in committing adultery, and then worsened when he lied to his wife and believed that she was blind to his behavior.
As the witchcraft accusations begin, Proctor believes that he can remain aloof from the increasing hysteria. He foolishly assumes that his hypocrisy is distinct from that of the other respected men in his community. Even though he knows that Abigail is targeting him, he refuses to intervene until Elizabeth is targeted. Knowing that she is likely to expose his adultery if he does not go public, he finally comes forward. The loss of his wife’s freedom finally makes an impact on him, but it can be argued that if she were not pregnant, he might not have stepped up even then. His cowardice almost certainly contributed to the speed and broadening scope of the proceedings, thereby helping send other innocent people to their death. Although he ultimately stops telling lies, in that he will not admit to witchcraft, by the time he takes an ethical stand, he is already powerless.
I think that Proctor's power changes over the play as his voice becomes more definite. I don't think that it is accident that Proctor's wish to become invisible and not be involved involves him not having power. In the first one and a half Acts, this is evident. Proctor is frustrated at not being heard both in public with others and with his own wife at home. It is only towards the end of the Second Act where Proctor's power begins to assert itself because Proctor begins to use his voice in defining his own world. When he says to Mary that his wife will not go to jail because of Abigail and he will do what he needs to free his wife, it is a moment where Proctor starts to show power because he activates his voice. When Proctor steadies Corey and the trial and shows support to Nurse, it is a moment when Proctor uses his voice and demonstrates his power. Even when he confesses to adultery in the trial, he does so to show power and in the process his voice or his "name" becomes something more evident. Certainly, by the end of the drama, Proctor might lack political power, but he represents a domain whereby power and autonomy are transcendent, something that even he knows might go beyond the temporal condition of Salem and represent what it means to possess power and voice, in a more universal sense.