Senators on the Foreign Relations Committee are grilling Secretary of State John Kerry over the deal that the P5+1 countries reached with Iran over its nuclear program.

Kerry was greeted with applause from a handful members from the radical CodePink group. But the mood changed immediately as Committee Chairman Sen. Bob Corker (R-Tenn) called the hearing to order.

Corker told Kerry he's "fairly depressed" after listening to the secretary answers to lawmakers' questions Wednesday, in a classified briefing. He compared the US negotiators who worked out a deal with Iran over its nuclear program to “a hotel guest who leaves only with his bathrobe.”

“You've been fleeced,” Corker said. “Instead of Iran being a pariah, you've turned Congress into a pariah. “

He added: “If we had dealt with dismantling Iran's nuclear program, our allies in the region would not react like they did.”

Kerry replied by saying that he believed there could be no better accord than the one that was reached, which he called was "a good deal for America, for the world and for our allies."

"We set out to dismantle [Iran's] ability to build a nuclear weapon and we achieved that," he said, calling the idea that a better deal could be reached to a unicorn, and saying "it's a fantasy."

When pressed by senators on the dangers posed b the deal, Kerry cited an article quoting former Israeli security officials, including Ami Ayalon, the former head of the Shin Bet, who suggested Israel's politicians were "playing with fears in a fearful society," and former Mossad head Efraim Halevy, who reportedly "hailed Obama's victory." He also cited Halevy as saying that the alternative to a deal with Iran would be military strikes that would "likely not be successful."

'You guys have been bamboozled'

Thursday's session, which started at 10:00 EST, pits Kerry - along with Energy Secretary Ernest Moniz and Treasury Secretary Jack Lew - against lawmakers, many of whom are hostile to the deal.

Lew told the senators Thursday that Iran is in "a massive financial hole" and would not be free to simply take of the money it is set to receive when sanctions are lifted and invest it in Hezbollah and other nefarious activity.

Sen. Jim Risch (R-Idaho) was not buying any of this and said: “Anyone who believes that this is a good deal really joins the ranks of the most naïve people on the face of this earth."

"We've been briefed that while Iran has been in this horrible financial condition, it supported Hezbollah, Hamas and the Houthis with every kind of aid there is," he continued. "These billions of dollars are going to be put back in their hands in nine months' time. This is a very heavy lift, trying to sleep at night knowing that you are going to release money, knowing that some of it will be used to try and kill Americans. With all due respect, you guys have been bamboozled and the American people are going to pay for that."

“Everyone here knows that there is a site called Parchin,” Risch added. “Parchin was designed and operated as an explosive testing site where they tested a detonation device for a nuclear weapon. Parchin stays in place and the IAEA can't even take samples there. How in the world can you have a nation like Iran doing its own testing? Even the NFL wouldnt go for that! We're going to trust Iran? This is absolutely ludicrous.”

Sen. Marco Rubio (R-Fla.) stated that once the economic sanctions against Iran are removed, they'll be impossible to snap back, and cited Iran's Foreign Minister Mohammed Javad Zarif as boasting as much. He noted that Iran will be allowed to develop ICBMs, “that know only one purpose” – to be fitted with a nuclear warhead. Those rockets “will be able to reach this room one day,” he warned.

“This deal is your deal,” he told Kerry, and Iran needs to know that “the next president is under no obligation to support it. The deal could go away on the day that President Obama leaves office.”

Rubio pointed to a section in the deal according to which the P5+1 countries will help Iran protect its nuclear facilities from sabotage, and asked if this means that the US will have to help Iran defend itself against possible Israeli cyber attack.

Kerry snickered and said he does not see “any way possible” in which this would happen. I assure you we will be coordinating every aspect of Israel's security.” He added, however: “I guess we'll have to wait until that point.”

Regarding Parchin, Senator Bob Menendez (D-NJ) asked: “Is it true that the Iranians are going to be taking the samples, because chain of custody means nothing if the original specimen is taken by the perpetrator.” Secretary Kerry said that the agreements regarding Parchin are part of the classified section of the deal, and that he trusts the IAEA when it says it is satisfied with them.

Congress vs. the White House

Congress can reject the deal, and keep the sanctions in place, but President Barack Obama can veto that decision. A hard-to-achieve two-thirds majority would be required to overturn the veto.

House Speaker John Boehner has already vowed Republicans would "do everything possible to stop" the agreement.

Concern has risen in Congress over the existence of “side agreements” between Iran and the International Atomic Energy Agency (IAEA) as part of the deal negotiated between Iran and world powers to regulate Tehran's nuclear program.

At least two Congressmen have expressed concern over the existence of these agreements, which they said the US was not privy to.

Meanwhile, officials in the Obama administration denied there were "secret side deals" in the Iran agreement.

In a statement Tuesday, Sen. Tom Cotton (R-Ark) and Rep. Mike Pompeo (R-Kansas) said they had been told by an IAEA official about the existence of these agreements, but that they would not be revealed to American legislators, who are now tasked with approving the Iran nuclear deal.

Pompeo told reporters that when he asked Secretary of State John Kerry about the codicils, he was told the US needed to “trust” the IAEA, a situation he called “unacceptable."

"I was incredibly surprised to learn there were components of the deal that Congress was not going to be privy to,” Pompeo and Cotton said in a statement.

White House National Security Adviser Susan E. Rice confirmed the existence of such documents, saying they had not been provided to House and Senate representatives because the US did not have access to them.