The P5+1 and Iran reached a deal yesterday on the Iranian nuclear program after very challenging processes and long negotiations between the parties. However, despite this deal, there are still significant challenges ahead for the parties in reaching a final agreement and the implementation of it. One of the potential difficulties lies in the domestic politics of the U.S., especially in the context of the tension between President Barack Obama and Congress. As we all know, while the round of negotiations were going on, U.S. Congress prepared a new sanctions package against Iran that Obama threatened to veto during his State of the Union speech last January. After this, Republicans in the Senate and House of Representatives made another move and invited Prime Minister Netanyahu of Israel, who opposed the possibility of such an agreement between the U.S. and Iran from the very beginning, to deliver an address to the joint session of the two chambers. Of course everybody already knew what would be the agenda of Netanyahu in his speech. Following this speech, which created a significant rift between the U.S. and Israel and was very quickly dismissed by the Obama administration, Republican members of the Senate this time did something that is not very common in U.S. foreign policy and wrote a letter directly to the leadership of Iran. The letter, signed by 47 Republican senators, basically warned the Iranian leadership that without an agreement that they would be able approve, the deal between Iran and the U.S. would be finished with a single order from the next president. This letter, in addition to the rift between the executive and the legislature also demonstrated that there is serious political polarization between Democrats and Republicans in regard to reaching a deal with Iran over nuclear issues. Senate Republicans demand the agreement be ratified by the Senate and be considered an international treaty, whereas the White House will probably go ahead and bypass the Senate at this point by naming it as an executive agreement. Some former presidents adopted this solution before, naming deals as executive agreements. However, after this tentative deal with Iran, the White House may try to convince Congress about this deal. An important reason of it is related to a recent Pew poll that shows that more Americans think that the Congress should have the final authority for approving the deal. The poll showed important findings about this issue. First of all, according to the poll, "more Americans approve (49 percent) than disapprove (40 percent) of the United States negotiating directly with Iran over its nuclear program." This shows important support for the Obama administration to pursue the deal. However, despite this support, the public remains deeply skeptical about the seriousness of Iranian leaders about implementing such an agreement. According to the poll, again, "Among those who have heard at least a little about the situation, 63 percent say Iranian leaders are not serious about addressing international concerns, compared with 27 percent who say they are. These opinions have not changed significantly since late 2013." Another significant finding of the poll is that the public predominantly thinks that Congress should have the final say in the agreement: "More say Congress (62 percent) than President Obama (29 percent) should have the final authority for approving any nuclear agreement between the U.S. and Iran." These numbers also show that if a final agreement is signed in July, the agreement will have serious ramifications during the presidential primaries of both parties next year and finally, the presidential race between Democrats and Republicans. All of the potential Republican candidates from the Senate were the signatories of the letter written to the Iranian leadership about the nuclear agreement. Hillary Clinton, however, who is probably the frontrunner among the potential Democratic presidential candidates, criticized the letter and said: "Either these senators were trying to be helpful to the Iranians or harmful to the commander-in-chief in the midst of high-stakes international diplomacy. Either answer does discredit to the letter's signatories."Of course this domestic political rift in the U.S. will also demonstrate itself during the implementation of the agreements, especially on the issue of the elimination of some of the economic sanctions against Iran in accordance with the final agreement. It would be a hard sell for Obama to convince Congress, which was planning to bring more sanctions on Iran during the negotiations, to remove some of these sanctions. Again, Obama can use a waiver to temporarily suspend these some of these sanctions, but it will be a temporary solution. Of course there is also a proposed legislation that would give a significant role for Congress to accept or reject removing the sanctions, and some Democrats also initially supported such a move to support the right of Congress to review the agreement. In fact, the deal between Iran and the U.S. can be the first step of a challenging process for the Obama administration.