Today was one of the most dramatic days of the trial, with startling admissions by the proponents’ two expert witnesses: Professor Kenneth Miller, testifying about the political power of gay people, and David Blankenhorn, testifying about the purposes of marriage.

The morning began with the conclusion of David Boies’s cross-examination of Professor Miller. Boies confronted Prof. Miller with several of Prof. Miller’s own earlier writings, which were highly critical of the ballot initiative process and particularly highlighted the risk that majorities will use the initiative process to target minority groups. Prof. Miller admitted that ballot measures can, and have, drawn upon anti-minority sentiment. Indeed, one of Prof. Miller’s own articles cited Proposition 22, the California initiative prohibiting marriage for same-sex couples that passed in 2000, as an example of such an anti-minority initiative.

Following the conclusion of Prof. Miller’s testimony, the afternoon was taken up by questioning of the proponents’ final witness, David Blankenhorn, the president of a private think tank called the Institute for American Values. Blankenhorn is best known as the author of a book called Fatherless America, in which he argued that fatherlessness is “the most harmful demographic trend of this generation” and the leading cause of “our most urgent social problems, from crime to adolescent pregnancy to child sexual abuse to domestic violence against women.” Blankenhorn is also one of the most visible and culturally influential opponents of marriage for same-sex couples.

The Prop 8 proponents asked Judge Walker to accept Blankenhorn as an expert in marriage, fatherhood, and family structures. But as plaintiffs’ attorney David Boies quickly made clear in his initial questioning, Blankenhorn lacked the usual qualifications for an expert witness in those areas. He has a bachelor’s degree in social science from Harvard and a master’s in the unrelated field of labor history from the University of Warwick in Coventry, England. He has no academic affiliation and has never taught at a college or university, and he has authored only two peer-reviewed publications, neither of which addressed marriage for same-sex couples. Judge Walker permitted Blankenhorn to testify, but noted that he might have ruled differently if this were a jury trial.

Charles Cooper (the lead attorney for the proponents) led Blankenhorn through what seemed to be a highly scripted presentation. Blankenhorn argued that the concept of marriage as “a socially approved sexual union between a man and a woman” is a “universal” definition that exists in every culture. He said the primary purpose of marriage is to make it as likely as possible that children will be raised by their biological parents.

Blankenhorn testified that he is opposed to allowing same-sex couples to marry because, in his view, that would promote the idea that the purpose of marriage is to serve the needs of adults rather than children. He also claimed that permitting same-sex couples to marry will lead to reduced rates of marriage by heterosexual people, higher rates of divorce, and more children born out of wedlock.

Blankenhorn did not claim to have any scientific data supporting that belief. Instead, he argued that letting same-sex couples marry might contribute to the “deinstitutionalization” of marriage, which he defined (rather vaguely) as any change that weakens “the rules” of marriage. He testified that marriage is a social institution, like baseball, and that when the rules are changed, fewer people will want to play. Blankenhorn stressed that he could not be sure that letting same-sex couples marry would have that effect, but he feared that it would.

Blankenhorn also noted that he supports domestic partnerships for same-sex couples as “a humane compromise.” In the past, he explained, he had not given the issue of domestic partnership much thought. But after being challenged by Jonathan Rausch (a conservative gay author) in 2007, he concluded that even if providing domestic partnership for same-sex couples might also contribute to the deinstitutionalization of marriage, considerations of fairness made it worth the risk.

For the last hour of the day, plaintiffs’ attorney David Boies began what is sure to be a dramatic and grueling cross-examination. Repeatedly, Blankenhorn bridled at Boies’s questions and often refused to answer them, leading to several interventions by Judge Walker instructing Blankenhorn to respond. The bulk of the cross-examination is still to come tomorrow, but thus far, Blankenhorn has acknowledged that letting same-sex couples marry would be beneficial to the couples and their children. He also admitted that there are no studies showing that children of same-sex couples are worse off than children raised by heterosexual parents.

Tomorrow will be the last day on which evidence will be presented. Judge Walker has announced that he will then take a few weeks to review the evidence before scheduling closing arguments in the case.