SAN FRANCISCO – Today begins Day 10, Week 3 of the federal trial challenging the constitutionality of California’s ban on same-sex marriages, Proposition 8.

The day will begin with the final presentations from the Ted Olson-David Boies legal team. They plan to present some documents and videotape. So far, they have used the introduction of videotaped evidence to great effect in the trial, showing expert witnesses from the other side making statements that undermine the other side’s case.

The other side, led by conservative Charles Cooper, will then begin to present its case in defense of Proposition 8.

While the Olson-Boies team called 17 witnesses to the court before U.S. district court Chief Judge Vaughn Walker, Cooper – at this point – has indicated he will bring only two or three.

One, who will likely take the witness stand this afternoon, is Kenneth P. Miller, an associate professor in the Department of Government at Claremont McKenna College. The second witness will be David Blankenhorn of a group called the Institute for American Values. The group’s website says it is an organization “contributing intellectually to the renewal of marriage” and “key American values.”

Miller’s testimony is expected to try and persuade the judge that gay men and lesbians are a politically powerful group. One of the criteria for deciding what level of scrutiny to apply to a law is whether the group the law targets for disparate treatment is a group that has little political power of its own to seek redress, such as at the ballot box.

Blankenhorn’s testimony is reportedly focusing on a key question in the case: What’s the purpose of Proposition 8? Laws have to have a purpose, although previous U.S. Supreme Court cases have signaled that the courts must give the legislatures and the voters considerable deference – the laws just need to have some simple rational justification. Blankenhorn is expected to say that justification is to promote procreation among straight couples and to “protect the children.”

Boies, who executed a stinging cross-examination of adverse witness William Tam last week, will cross-examine both of the defense’s experts this week.

On Sunday night, there was a report circulating that the defense might call a third witness – Frank Shubert, the Yes on 8’s paid campaign consultant and the man credited with constructing the successful anti-gay ballot campaigns in both California in 2008 and in Maine last November. The courtroom will, no doubt, be very crowded should Shubert take the stand.

The judge announced last Friday that the trial would not move straight into closing arguments after the evidence is presented. Instead, he will take “several weeks” to review the testimony and documents and formulate questions to pose to the legal teams during those closing arguments.

Olson said last Friday that he would be delivering the closing arguments for the plaintiffs, two same-sex couples who seek to obtain a marriage license. Also delivering a closing argument on behalf of the city of San Francisco, which is also a party to the case challenging Proposition 8, is Therese Stewart, the Chief Deputy City Attorney for the city. Cooper is expected to do so for the Yes on 8 team defending the law.