WASHINGTON (AP) — The Supreme Court began its election-year term Monday by wrestling over whether states must allow criminal defendants to plead insanity.

The one minor surprise when the justices took the bench just after 10 o'clock was the absence of Justice Clarence Thomas. The 71-year-old Thomas was at home, likely with the flu, the court said.

Justice Ruth Bader Ginsburg was in her customary seat to the left of Chief Justice John Roberts. The 86-year-old Ginsburg asked the first question in the insanity arguments.

Ginsburg was treated this summer for a tumor on her pancreas.

Meeting for the first time in public since late June, the court opened a term that could reveal how far to the right and how fast the court's conservative majority will move, even as Roberts has made clear he wants to keep the court clear of Washington partisan politics. The court is beginning its second term with both of President Donald Trump's Supreme Court appointees, Justices Neil Gorsuch and Brett Kavanaugh, on board.

The justices could be asked to intervene in disputes between congressional Democrats and the White House that might also involve the possible impeachment of the Republican president .

Roberts would preside over a Senate trial of Trump if the House were to impeach him.

Its biggest decisions, in cases involving abortion, protections for young immigrants and LGBT rights, are likely to be handed down in late June, four months before the election.

The case about an insanity defense comes from Kansas, where James Kraig Kahler was sentenced to death for killing his estranged wife, two teenage daughters and his wife's grandmother.

Kahler wanted to mount an insanity defense, but Kansas is one of four states that eliminated a defendant's ability to plead not guilty by reason of insanity. Idaho, Montana and Utah are the others. Alaska also limits the insanity defense.

It was unclear how the case would come out. Justice Elena Kagan suggested that even if Kahler were to win at the Supreme Court and could plead insanity, he ultimately would not get a reprieve from his conviction. In no state, she said, "would your client be found insane."

The justices also were hearing arguments Monday in a challenge to a murder conviction by a non-unanimous jury in Louisiana.