Washington ? Sen. Barack Obama said Monday he was still willing, if elected, to meet with Iranian leader Mahmoud Ahmadinejad because “strong presidents talk to their enemies.”

The Democratic front-runner, Sen. Hillary Clinton, D-N.Y., called for a “vigorous diplomatic effort” with Tehran starting with lower-level U.S. officials.

Ahmadinejad’s controversial speech at Columbia University Monday reverberated across the 2008 presidential campaign trail, with both Republican and Democratic candidates denouncing the Iranian president as a Holocaust denier and Israel hater.

Obama, D-Ill., a Columbia graduate, said he “probably would not have invited” Ahmadinejad to speak there, but he said he remained willing to meet with the leaders of hostile nations, without precondition, in the first year of his presidency.

“By us listening to the views even of those who we violently disagree with, that sends a signal to the world that we are going to turn the page on the failed diplomacy that the Bush administration has practiced for so long,” said Obama.

This summer, Clinton called Obama’s willingness to meet with hostile leaders without conditions “irresponsible and frankly naive.” She said Monday there needs to be aggressive diplomacy with Iran.

“You don’t start with the president,” she said. “You start at the embassy level, you start with all kinds of emissaries, but it has to be ongoing.”