Moving on to Greenwald's main point:
Is this supposed to pass for analysis? Tom Schaller has an unpublished chart with no underlying data and that settles that? I based my claims on an extensive interview with a PhD expert in the field of dynastic succession and nepotism, and then published a separate interview with him as a podcat. He says the exact opposite of Schaller:
I don't know what explains the discrepency -- though Schaller's chart only counts relatives in Congress, not ones in other key positions such as Governorships.
Let's take these things bit by bit.
First, I recommend the interview (transcript is here). Burroughs has some interesting things to say.
Second, Tom Schaller (also a Ph.D.!) tells us exactly where his data come from (an IPSCR data set). I'd like to read the whole article, which he does not link to, but really I trust Schaller to correctly report one variable, and I trust the IPSCR data sets.
Third, the differences between Schaller and Burroughs are simple enough to understand: their time periods are different. Schaller is looking at the entire history of the Senate through the 104th Congress; Burroughs makes no claims at all about anything before WWII, but he does look at more recent Congresses. Burroughs sees an increase since the 1950s from about 14 Senators (which seems consistent with Schaller's graph) to a peak of 24 recently. What Schaller has, on the other hand, looks to my eye like a flat period from the 81st Senate (1949-1951) until a decline in the 1990s. So that leaves a question or whether Burroughs is capturing something Schaller doesn't in the 1960s-1990s, and another question about the current decade.
What Burroughs doesn't confirm, however, is Greenwald's claim that the recent period is anything new; Schaller's data make it pretty clear that the recent surge, assuming there has been one, is still to historically low levels. Moreover, methodology differences here would tend cut against Greenwald's claims. Schaller is just looking at family in Congress, while Burroughs is also including "political families" in general (I'm not sure how he defines it, but it appears to be those with family members in elective office or formal party positions. On the other hand, if he only includes immediate family members, then he may be missing some grandchildren included in Schaller's numbers, or at least in my quickie look at 1929).
What about the White House? Here, I'll somewhat disagree with Burroughs. For Burroughs, "If you look at it since the 1970s, the people who've won the presidential nominations, and particularly the elections, have much more often been from more famous families." Well, yes, the two George Bushes were elected. Beyond that, however...Carter, Reagan, Clinton, and Obama are not from "famous families" -- in fact, Reagan, Clinton, and Obama could not have had more obscure beginnings. The main losing nominee who falls in the "famous family" category is Al Gore, but the other losers, McGovern, Ford, Mondale, Dukakis, Dole, Kerry, and McCain were as far as I know the first of their family to have political careers. This doesn't seem exceptional to me at all. In the previous generation, Democratic nominees Roosevelt, Stevenson, and Kennedy were all from political families. Hillary Clinton came close...and so did Taft, more than once. Gore was Vice President, and Lodge was Nixon's VP nominee.
Obviously, the Bushes constitute an important data point, but outside of them I'm not seeing anything definitive in these stories, either.
(There have been a lot of moderately successful and unsuccessful presidential candidates recently who are nepotism type cases: Pat Robertson, Mitt Romney, Liddy Dole, and others. It's hard to compare the field of presidential candidates post-1972 with pre-1972 fields for technical reasons; until 1972, many candidates, including serious candidates, never announced for president, so it's hard to know who constitutes the field of candidates in 1952 or 1960).
I'm certainly not convinced that there's a historically unusual surge of dynastic candidates in the last decade. However, I am interested in whether there's been something of a resurgence to higher levels than existed in the postwar period. Perhaps Schaller can update his chart?