In The Great Gatsby, power is often associated with money. He or she that has money has power. George Wilson is one of the weaker people in the novel and he is also one of the poorest. George has a run down shop and he lives in the vicinity of the Valley of Ashes, a drastically different setting than the nicer areas of East and West Egg. George's wife, Myrtle, is having an affair with Tom Buchanan. Part of the attraction, for Myrtle, is that Tom is relatively wealth. Therefore, Tom has a certain kind of power in terms of wealth and attractiveness (albeit to the shallow Myrtle) and this all stems from him having money.
Gatsby's parties attract people because his parties have become a gathering place for social elites. They go to his parties, not because they admire Gatsby or even know him, but because the parties are a place for socializing among the wealthy and/or popular people in the city. There, people party but also make connections and in that elitist circle, the rich consort with the rich and look out for each other's well-being (mostly in terms of money): thereby, the rich stay rich and the poor stay poor. Gatsby is able to host these parties because he has a nice house which came from his own wealth. People like George Wilson would never be found at such a party, nor would he think that he might be invited or encouraged to come.
Daisy also is attracted to money. This is part, possibly the biggest part, of the reason she married Tom. And even though Gatsby is a romantic and an idealist, he is a realist in the sense that he recognizes the power inherent in money in the social circles that he wants to live in (namely, Daisy's social circles). So, Gatsby realizes that he needs money to win her over. When he returns to find Daisy has married Tom, his idealism and romanticism remain; these qualities push him to that realist realization in that he would need money to win Daisy back from Tom. This becomes Gatsby's strategy: become wealthy, stay close to Daisy, and try to become what he thinks Daisy will admire. Note that Gatsby's romanticism and realism, the dichotomy, lead to his downfall. He is driven by that romanticism to win Daisy back, but he knows that he must have money to do so. If they were truly meant to be together, the money would not be necessary. However, in this society, the American Dream is imperfect. Gatsby resorts to illegal means to obtain his wealth. Gatsby idolizes Daisy as some perfect mate even though he must know that Daisy is attracted to money, not just the idea of love. Gatsby makes it plain that he realizes this flaw in Chapter 7 (but this doesn't seem to affect his love for Daisy). Nick begins, Gatsby responds, and Nick analyzes what Gatsby has said:
“She’s got an indiscreet voice,” I remarked. “It’s full of——” I hesitated.
“Her voice is full of money,” he said suddenly.
That was it. I’d never understood before. It was full of money—that was the inexhaustible charm that rose and fell in it, the jingle of it, the cymbals’ song of it. . . . high in a white palace the king’s daughter, the golden girl. . . .
The whole notion of Gatsby's American Dream (winning Daisy) is conflated with the idea of money and wealth. Therefore, the power to obtain this dream, among other things, is achievable through wealth. This notion makes the idealism of Gatsby's love flawed and it also suggests that success is necessarily linked to wealth, caused by it, or related to it in some way.