But his dissent stands out for how much it subscribed to the Trump worldview of fraud, a notion debunked by election law experts and that has failed overwhelmingly in dozens of state and federal court challenges.

"An election free from strong evidence of systemic fraud is not alone sufficient for election confidence," Thomas wrote.

In his 11-page dissent on Monday, Thomas referred to "fraud" 10 times and emphasized alleged flaws in ballots that arrive by mail.

But if you're going to ignore the fact that there were states that did not follow their own state legislatively set laws, that's the issue at heart."

Election experts reject such contentions, and former Attorney General William Barr, a Trump appointee, said in December the Justice Department found no evidence of widespread fraud in the 2020 election.

The constitutional question with Pennsylvania

The Supreme Court has generally sidestepped Trump election controversies, and even as Justices Samuel Alito and Neil Gorsuch dissented and said the majority should hear the Pennsylvania dispute to clarify rules for the future, they declined to mention fraud or voter irregularities on the ground and did not join Thomas' dissent.

"Because the Federal Constitution, not state constitutions, gives state legislatures authority to regulate federal elections," Thomas wrote, "petitioners presented a strong argument that the Pennsylvania Supreme Court's decision violated the Constitution by overriding the clearly expressed intent of the legislature."

Thomas observed that the state court's decision involved too few ballots to affect the outcome of any federal election.

"An election system lacks clear rules when, as here, different officials dispute who has authority to set or change those rules," Thomas wrote.

competing candidates might each declare victory under different sets of rules."

Pennsylvania state election officials enforced the state court deadline and, under a prior court order, segregated the late-arriving ballots, of which there were only about 10,000, according to the secretary of state's office.