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The topic of 'nepotism' in politics is closely related to broader questions of elite-favoring mechanisms in politics more generally. Many people use the term "nepotism" to discuss things like the aforementioned cases of direct manipulation of office to install a relative, etc., but it doesn't address the broader topic of why some people are much more likely to get involved in or succeed in political aspirations.
As a democracy, we just don't have many institutions and mechanisms to train ordinary people in the processes of running for office, outside political parties (and their limitations), nor do we have much of an organized system of public financing of elections.
If running for office is the province of the initiated, and if it's more likely to be a successful option for those who can most easily access the financing needed, then it's a system to promote a general preference for individuals with direct connections to established insiders and to sources of funding based in more concentrated wealth.
So to the extent that blogs & internet-connected activists do so, they're actually attempting to plug a huge gap in the U.S. system of democracy.