The United States will respond firmly if Iran fails to ho**r the accord aimed at curbing its nuclear program, President Barack Obama said Friday, as he works to win over undecided US lawmakers. "We have a wide array of unilateral and multilateral responses that we can employ if Iran fails to meets its commitments," Obama said in a letter dated August 19 and sent to Jerrold Nadler, a Democrat in the House of Representatives who an**unced that he will vote to approve the accord. In his letter released by the White House, Obama reiterated his view that the accord reached last month in Vienna is good for the United States, Israel and the Middle East in general.