As U.S. Secretary of State John Kerry and Western envoys meet with Iran's foreign minister, part of a renewed push to get Iran to agree to a deal on its nuclear program, lawmakers in Washington are watching closely.
In the U.S. Capitol, the much-talked about recent Iranian "charm offensive" on the West seems to be falling on deaf ears. Lawmakers, like the Senate Armed Service Committee's James Inhofe are skeptical of Iran's sincerity.
"They're our enemies. They hate us. And anything that's going to be predicated on our trust of these people isn't going to work," said Inhofe.
A group of 11 Republican senators has sent U.S. President Barack Obama a letter, urging him to increase pressure on Tehran, warning that despite Tehran's diplomatic softening, "Iran has not changed course."
And it's not only members of the Republican Party, often at odds with Obama, who are expressing doubts.
Iranian President Hassan Rouhani's speech this week at the United Nations failed to impress some Democrats, like Senate Foreign Relations Committee Chair Robert Menendez.
“I heard a lot about peace, which we of course seek to embrace. But it is very hard to be promoting peace when you are rushing to powerful nuclear weapons,” said Menendez.
Such wariness could be a big problem for Iran as it tries to convince the international community the time has come to ease sanctions - as many U.S. sanctions cannot be undone without Congressional approval.