President Obama is expected to nominate Elena Kagan to the Supreme Court today.

When Ms. Kagan became United States solicitor general, the federal government’s top appellate lawyer, in March 2009, she had argued no cases in the United States Supreme Court and had, indeed, just recently become a member of its bar.

Six months later, she made her debut in a case that would turn out to be one of the court’s biggest decisions in recent years, Citizens United v. Federal Election Commission.

She lost.