An open letter to Iran by 47 Republican members of the United States Senate released Monday started a heated debate this week. The question was: Who controls foreign policy -- Congress or the president?

　　The letter warned Iran that any deal over its disputed nuclear program with the Obama administration could be overturned. It said that the next U.S. president "could revoke such an executive agreement" and "future Congresses could modify the terms of the agreement at any time." Without congressional approval, the letter said, the agreement would be only an executive agreement.

　　Lawmakers signing the letter included all but seven of the Republican Party's 54-member majority in the U.S. Senate. They noted that President Barack Obama was leaving office in less than two years, as required by the Constitution. Many of them, they said, might still be in office for many years.

　　Historically, presidents and Congress have argued over their constitutional powers to control foreign policy. Thomas Fleming is a historian who writes about American history. He says America's first president had a strong opinion on the responsibility of the executive branch in foreign policy.

　　"Washington's presidency was the strong president personified. He was barely in the chair of the presidency more than a few days and he wrote a letter to all the nations of Europe saying ‘if you want to communicate with the United States of America, write a letter to me, George Washington, not to the Congress.'"

　　President Obama criticized the letter to Iran on Monday. A spokesman for the president, Josh Earnest, told reporters the letter was an attempt to slow down the sensitive negotiations. The U.S. and five other world powers are trying to reach a basic agreement with Iran. The goal is to persuade Iran to give up its program to develop nuclear weapons in return for easing of international sanctions.

　　Republican Senate Majority Leader Mitch McConnell of Kentucky was one of the lawmakers to sign the letter. He defended it, saying he did not know why the administration wanted to keep Congress out of the emerging deal with Iran. He said it was clear that the president did not want Congress to have a part in a deal that could have a big effect on U.S. national security.

　　The letter brought strong reactions from former and current diplomatic officials. Democrat Hillary Clinton has served as both a U.S. senator and a U.S. secretary of state. She said the letter was out of step with the best traditions of the Senate.

　　U.S. Secretary of State John Kerry said on Wednesday that the letter left him in "disbelief."

　　"This risks undermining the confidence that foreign governments in thousands of important agreements commit to between the United States and other countries. And it purports to tell the world that if you want to have any confidence in your dealings with America they have to negotiate with 535 members of Congress."

　　Not all Republican Senators agreed with the letter. Earlier in the week, Senate Foreign Relations Committee Chairman Bob Corker did not think the letter would help to get a bill that would require Congress to advise on a possible nuclear deal with Iran and possibly lifting sanctions at an appropriate time. And Senator Susan Collins of Maine told VOA that she did not think the letter was the right thing to do.

　　Iranian officials also responded to the letter. Iran's supreme leader, Ayatollah Ali Khamenei said the move showed "disintegration" in U.S. politics. Iranian Foreign Minister and chief negotiator Mohammed Javad Zarif dismissed the letter, saying it was of "no legal value."

　　Talks are set to restart on Sunday. Negotiators are seeking to complete the basic deal by the end of March, with final agreement by the end of June.

　　Whether the U.S. can reach a nuclear agreement with Iran, one thing is clear. The U.S. Constitution states that the President of the United States "shall have Power, by and with the Advice and Consent of the Senate, to make Treaties."

　　I'm Christopher Jones-Cruise.

　　VOA Congressional Correspondent Cindy Saine reported this story. Mario Ritter wrote it for VOA Learning English. Hai Do was the editor.