WASHINGTON – Sen. Bob Casey (D., Pa.) hammered Senate Republicans' controversial letter to Iranian leaders Wednesday, calling it "reckless."

"This is a misguided and reckless attempt to circumvent a sitting U.S. President by going directly to the leader of the Iranian regime – a longtime adversary of the United States. It is clear that many Americans find it offensive," Casey said in a statement, joining the still simmering fight in unusually strong terms.

Casey previously sat on the Senate foreign affairs committee and chaired the subcommittee focused on the Middle East. He has signed on as a co-sponsor of a plan to impose new sanctions against Iran, despite White House appeals to wait as the U.S. and other countries negotiate with Iran over the country's nuclear weapons program.

But he joined other Democrats in criticizing the letter led by Sen. Tom Cotton (R., Ark.) and signed by 46 other Republicans, including fellow Pennsylvanian Pat Toomey.

"No one has been tougher on this issue than I," Casey wrote. "We should be focusing on bipartisan policy, not engaging in partisan theatrics."

Cotton and fellow Republicans wrote Iranian leaders saying any nuclear deal could be wiped out by a future administration or Congress, effectively discouraging Tehran from signing an agreement with President Obama. Cotton, Toomey and others who signed the letter say they are hoping to prevent a bad deal that would leave Iran with a path toward obtaining a nuclear weapon, as Israeli Prime Minister Benjamin Netanyahu has warned and even some Democrats have worried about.

Cotton has said that Congress should have the chance to approve any deal Obama strikes with Iran, and that the people who signed the letter were "simply speaking for the American people."

But Democrats and some Republicans have railed against the letter, calling it an unprecedented attempt to undercut the president.

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