From a Los Angeles Times blog:

It was a pivotal moment in the presidential campaign, when Hillary Rodham Clinton branded Barack Obama as “naive” for suggesting he would meet with the leaders of Iran, Syria, Venezuela, Cuba and North Korea in his first year as president without any preconditions
“I thought that was irresponsible and frankly naive,” Clinton said after their July 2007 debate in South Carolina, adding that Obama gave an answer “I think he is regretting today.”
During his inaugural address, Obama maintained his outreach to Tehran, where President Mahmoud Ahmadinejad has denied both the Holocaust and Israel’s right to exist. In one of the most discussed passages of his speech, Obama said,
To those who cling to power through corruption and deceit and the silencing of dissent, know that you are on the wrong side of history, but that we will extend a hand if you are willing to unclench your fist.
Today, Obama spoke for a growing cadre of powerful nations — France, Britain, Germany and for the first time perhaps even Russia — in condemning Iran. Amid intelligence that Iran has kept a second nuclear facility, capable of producing 3,000 centrifuges, hidden from weapons inspectors for years, Obama warned that unless Iran acts immediately, punishment will be swift. “Iran is breaking rules that all nations must follow,” he said.