WASHINGTON (Reuters) - The U.S. Supreme Court on Tuesday appeared ready to rule against a Puerto Rican politician who maintained he cannot be retried on corruption charges involving a trip to Las Vegas to watch a boxing bout after his original conviction was thrown out.

U.S. Supreme Court is seen in Washington, U.S., October 3, 2016. REUTERS/Yuri Gripas

The eight justices heard the first oral argument of their new term in the appeal filed by Hector Martinez Maldonado, who served in Puerto Rico’s Senate from 2005 until his 2011 conviction, and businessman Juan Bravo Fernandez, former president of a private security company.

Several justices expressed skepticism about the defendants’ arguments.

Bravo Fernandez sought to bribe Martinez Maldonado to win passage of bills that would benefit his business, according to prosecutors. The case focused in part on allegations that Bravo Fernandez paid for Martinez Maldonado to travel to Las Vegas in 2005 to watch boxer Felix “Tito” Trinidad, a sports hero in the Caribbean U.S. territory, lose to underdog Winky Wright.

Bravo Fernandez and Martinez Maldonado were convicted for their roles in the alleged bribery scheme. The Boston-based 1st U.S. Circuit Court of Appeals threw out their convictions in 2013.

Federal prosecutors planned a new trial but the two men said it should be barred because it would violate the U.S. Constitution’s protection against “double jeopardy,” preventing people from being tried on charges for which they already have been acquitted.

Their lawyers said double jeopardy applies because the jury had acquitted them on some of the criminal charges concerning conduct closely related to the actions on which the retrial would be focused. Prosecutors said the acquittals were inconsistent with the convictions, suggesting jurors did not understand the law.

Based on the questions they asked, the justices appeared unlikely to throw out a 2015 appeals court decision backing prosecutors.

Justice Elena Kagan asked the defendants’ attorney, Lisa Blatt, about her argument: “Is it anything more than rhetoric?”

Chief Justice John Roberts told Blatt it was her burden to show the jury’s verdict was a legal and valid judgment on the same set of facts that the government wants to re-try, and not just a misunderstanding.

A ruling is due by the end of June.

Outside the courthouse, protesters demanded that the U.S. Senate confirm Merrick Garland, President Barack Obama’s nominee to fill the court’s vacancy left by the February death of Justice Antonin Scalia. Senate Republicans have refused to act on Garland’s nomination, saying Obama’s successor should make the appointment after taking office in January.