WASHINGTON (AP) — The Supreme Court began a potentially contentious election-year term Monday in seeming general agreement that juries in state criminal trials must be unanimous to convict a defendant.

The justices took up a quirk of constitutional law, a 47-year-old ruling that requires unanimity in federal, but not state trials. Earlier in the day, the court also wrestled with 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.

Those cases probably will highlight the divisions on a court made up of five conservatives appointed by Republican presidents and four liberals named by Democrats.

But on Monday, conservative and liberal justices appeared to agree that the same rules should apply in federal and state trials. They heard arguments in an appeal by a Louisiana man who is serving a life term for killing a woman after a jury voted 10-2 to convict him. Oregon is the only other state that allows for non-unanimous convictions for some crimes.

Louisiana voters have changed the law for crimes committed beginning this year.

The court has formally held that most of the Bill of Rights applies to states as well as the federal government, but it has not done so on the Sixth Amendment's unanimous jury requirement.

"What about the constitutional rights of people in prison?" Gorsuch asked Louisiana Solicitor General Elizabeth Murrill, who argued that the state's court system could be inundated with claims if the justices rule against Louisiana.

A decision for defendant Evangelisto Ramos would result in his conviction being overturned and also would affect defendants who are still appealing their convictions. But the court is not expected to say anything about defendants whose cases are final. It would take another round of lawsuits to figure that out.

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."