White House Chief of Staff Denis McDonough said Sunday he thinks Iran's election of moderate reformer Hassan Rouhani as the country's next president is a "potentially hopeful sign."

"I think the question for us now is, if he is interested in, as he has said in his campaign events, mending Iran's relations with the rest of the world, there's an opportunity to do that," McDonough said on CBS's "Face The Nation." "If he lives up to his obligations under the U.N. Security Council resolution to come clean on this illicit nuclear program, he will find a partner in us, and there will be an opportunity for that."

But, McDonough added, "to get that point, we need him to live up to the obligations on the nuclear program. And if he does, I think there's a great opportunity for Iran, and the people of that storied country, to have the kind of future that they would I think justifiably want."

Iran this weekend elected Rouhani, a Shiite cleric who campaigned on a pledge of “reconciliation and peace.”

Sen. Marco Rubio (R-Fla.) said he didn't have high hopes the election would make Iran easier for the United States to deal with.

"I'm not all that optimistic," Rubio said on ABC's "This Week With George Stephanopoulos." He added: "Unfortunately, this gentleman who was just elected is a strong supporter of the nuclear program and the nuclear weaponization as well."