I agree with Peter. As for your follow-up questions, "mobilize" is a word commonly used in politics, which in that context means to take political action, particularly within a particular group. If you "mobilize" a group of voters, it's like getting them to go out and vote or maybe getting them to go out and campaign or take other political action. "Proportion" refers to the percentage of people. So in this case, as Peter said, white evangelicals are a small percentage (or "proportion") of the population, only 15%. However, they have "mobilized" themselves to be very politically active, and to make up a much higher percentage/proportion of the electorate (aka, people who vote) at 25%. So they have mobilized themselves to be a higher proportion among voters compared to their proportion in the population.