Elena Kagan sworn in as Supreme Court justice

Elena Kagan was sworn in as the 112th justice of the Supreme Court on Saturday, opening the first era in U.S. history with three women serving on the nation’s premier judicial bench.

Chief Justice John G. Roberts Jr. administered the oath at the Supreme Court just two days after the Senate’s 63-37 vote Thursday to confirm her nomination and one day after President Obama hosted a White House reception in Kagan’s honor.

She is not expected to dramatically change the ideological balance of the court because she replaces retired Justice John Paul Stevens, a fellow liberal jurist.

But her installation marks a historic demographic milestone. Women now make up one-third of the nine-member court, with Kagan joining Sonia Sotomayor and Ruth Bader Ginsberg as an associate justice. The first and only other woman on the court was Sandra Day O’Connor, who served from 1981 to 2006.

At Friday’s reception, Obama said that the addition of another woman ensures that the court will be “a little more inclusive, a little more representative — more reflective of us as a people than ever before.”

However, with Kagan — a Jewish law professor who studied at Harvard Law School — the court becomes less diverse in other ways. It no longer has a single Protestant, and all nine justices have been trained in the Ivy League.

Having served for the last year as Obama’s solicitor general, Kagan has been the government’s chief lawyer before the court. At the White House reception, Kagan told her Justice Department associates not to expect her to be a rubber stamp for the administration.

“Once I put on that robe, I’m only going to vote with them when they have the better of the argument, which — let’s be frank — is not in every case,” Kagan said to laughter.

Kagan is expected to recuse herself from deciding several upcoming cases before the court because she participated in preparing the government’s position.

In Saturday’s low-key ceremony, Kagan first took a constitutional oath, which is administered to all federal officers. In a second judicial oath, she swore to “administer justice without respect to persons, and do equal right to the poor and to the rich.”