More: 150,000 sign treason petition on US Republican letter to Iran - Yahoo Finance (March 11, 2015)According to the petition, the 47 senators "committed a treasonous offense when they decided to violate the Logan Act, a 1799 law which forbids unauthorized citizens from negotiating with foreign governments."
Critics argue that the lawmakers, including at least three potential Republican 2016 presidential candidates, broke the law, or at least violated the traditions of Congress, by directly engaging a foreign power on US foreign policy.
It must be near impossible for the US to have a coherent and sensible foreign policy when said policy is independently made by both the ruling party and the opposition.
This incident with the letter should be seen in the context of Israeli PM Netanyahu's visit and speech to the US Congress, the invitation for which the same Republican senators had no doubt been involved in.