advisory group comparable to a think-tank that Francis appointed to guide him on a wide range of public policy issues.

Back home, Clinton holds a significant delegate lead against Sanders, but the senator has vowed to stay in the campaign until the party's July convention. His message calling for a political revolution to address wealth inequality and the influence of Wall Street on U.S. politics has galvanized many Democrats and independents.

Despite being enmeshed in an increasingly bitter campaign against Clinton, Sanders aides said the trip was not aimed at appealing to Catholic voters who comprise a large share of the Democratic electorate in New York and an upcoming contest in Pennsylvania.

The Vatican has been loath to get involved in electoral campaigns and usually tries to avoid any perception ofpartisanship involving the pope. Popes rarely travel to countries during the thick of political campaigns, knowing a papal photo opportunity with a sitting head of state could be exploited for political ends.

As a result, the invitation to Sanders to address the Vatican conference raised eyebrows and allegations that the senator lobbied for the invitation.

The chancellor for the pontifical academy, Bishop Marcelo Sanchez Sorondo, has said he invited Sanders because he was the only U.S. presidential candidate who showed deep interest in the teachings of Francis.

Other attendees included Morales of Bolivia and President Rafael Correa of Ecuador, along with Cardinal Oscar Rodriguez Maradiaga of Honduras, a member of the academy, and Columbia University professor Jeffrey Sachs, an adviser to the United Nations on environmental and sustainability issues. Sachs has