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Washington • Sens. Mike Lee and Orrin Hatch joined 45 fellow Republicans in signing an open letter to Iran's leaders, reminding them that President Barack Obama's term will expire in two years and whatever deal he strikes with the country could be upended.

The White House warned that the letter, a rare intervention by America's legislative branch in foreign affairs, could hurt the ongoing talks with Iran trying to reach an agreement over limits to its nuclear program.

"I would describe this letter as a continuation of a partisan strategy to undermine the president's ability to conduct foreign policy and advance our national security interests around the globe," White House Press Secretary Josh Earnest said Monday.

The president told reporters Monday that he finds it an odd to see conservatives in Congress lining up with hardliners in Iran's government, but he won't let it detract from his goal of getting a workable agreement.

"I think it's somewhat ironic to see some members of Congress wanting to make common cause with the hardliners in Iran. It's an unusual coalition. I think what we're going to focus on right now is actually seeing whether we can get a deal or not. And once we do — if we do — then we'll be able to make the case to the American people, and I'm confident we'll be able to implement it," Obama said.

The letter, written by freshman Arkansas Sen. Tom Cotton, is addressed to the "Leaders of the Islamic Republic of Iran," and begins by saying that the leaders may not "fully understand our constitutional system" and that Congress plays a significant role in ratifying international agreements.

"President Obama will leave office in January 2017, while most of us will remain in office well beyond then – perhaps decades," the letter says.

Any agreement between Iran and the Obama administration would be "nothing more than an executive agreement," the missive says, adding that, "The next president could revoke such an executive agreement with the stroke of a pen and future congresses could modify the terms of the agreement at any time."

Earnest said the letter would "throw sand in the gears" of the negotiations and isn't helpful. The White House was similarly irked recently when House Speaker John Boehner invited Israeli Prime Minister Benjamin Netanyahu to speak before a joint meeting of Congress at the same time Secretary of State John Kerry was negotiating with Iran to halt its nuclear operations.

Lee's office said the first-term senator has no regrets about signing onto the letter.

"He believes that the tentative agreement with Iran, involving sanctions that were passed by Congress, should be approved or disapproved by Congress. Any agreement that does not have the Congress' support could easily be changed by the next president, and all sides need to understand this as negotiations progress," said spokesman Brian Phillips

Hatch's office did not immediately respond to questions about the letter.

Iran said the letter would have no impact on the talks and dismissed it as a "ploy."

"In our view, this letter has no legal value and is mostly a propaganda ploy," Javad Zarif, the Iranian foreign minister, said, as quoted by The New York Times. "It is very interesting that while negotiations are still in progress and while no agreement has been reached, some political pressure groups are so afraid even of the prospect of an agreement that they resort to unconventional methods, unprecedented in diplomatic history."

Senate Democratic Leader Harry Reid said the letter was evidence "Republicans don't know how to do anything other than attempt these seemingly juvenile political attacks against the president."