Why are some Interest Groups more important than others in the USA?

Interest groups have varying influence for a range of factors. Some of the main reasons for this are: the ability of interest groups to bring in money, the ability of interest groups to attract supporters, how active the supporters are and how easily the interest group fits into mainstream politics. Overall, although all of these factors have some influence in how powerful interest groups are, due to the distinct nature of the USA's system which allows money to influence the USA's political institutions to a great extent, money is the main reason for the importance of interest groups.