Secretary of State John Kerry spent five minutes of a Senate hearing excoriating a group of 47 Republicans who sent a highly unusual letter to the government of Iran warning that Congress could modify the terms of any nuclear deal it negotiates with the White House.

'This letter raises questions of judgment and policy,' he insisted, before Tennessee Republican Sen. Bob Corker cut him off and scolded him for delivering 'a well-written speech.'

'It's not a speech! This is not a speech!' Kerry erupted. 'This is a statement about the impact of this irresponsible letter. The letter does not have legal authority, and I think you have to ask what people are trying to accomplish.'

Kerry later staked out a position that lawmakers have no standing to change any nuclear agreement between the U.S. and Iran because it won't be 'legally binding' in the first place.

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Secretary of State John Kerry testified on Capitol Hill in Washington on Wednesday, saying Congress won't have a role in determining the terms of a nuclear deal with Iran because the agreement isn't 'legally binding'

A Code Pink protester holding a sign saying 'There is no military solution' in the Middle East was removed from Wednesday's hearing after heckling Kerry

IT'S A NICE SPEECH: Tennessee Sen. Bob Corker scolded Kerry for lecturing his former Senate colleagues about the role of Congress in ratifying deals with other countries

'We've been clear from the beginning: We're not negotiating a, quote, "legally binding" plan,' Kerry told the Senate Foreign Relations Committee.

'We're negotiating a plan that will have in it the capacity for enforcement. We don't even have diplomatic relations with Iran right now.'

He blamed Arkansas Republican Sen. Tom Cotton and 46 other GOP senators for signing a letter on Monday that 'ignores more than two centuries of precedent in the conduct of American foreign policy.'

Kerry, America's top diplomat and the Obama administration's senior Tehran negotiator, said he reacted with 'utter disbelief' to the letter, which also warned Iran's leaders that an accord with President Barack Obama's team could expire the day he leaves office.

The letter itself is an unprecedented intervention by Congress into negotiations with a foreign power, Kerry suggested.

'During my 29 years in the Senate I never heard of, or even heard of it being proposed, anything comparable to this,' he said.

'This letter ignores more than two centuries of precedent in the conduct of American foreign policy.'

'When it says that Congress could actually modify the terms of an agreement at any time is flat wrong,' said Kerry, who once chaired the committ he addressed on Wednedsay.

'You don't have the right to modify an agreement reached executive to executive between leaders of a country.'

Cotton, a freshman senator, does not sit on the Foreign Relations panel.

The administration has been forced into a no-win situation in the Middle East, with the so-called 'Islamic State' gaining territory in Iraq while the Iranians help push them back.

'They want us to destroy ISIS. They want to destroy ISIS,' Kerry said during an exchange with Florida Republican Sen. Marco Rubio.

'ISIS is a threat to them,' he said of Iran. 'It is a threat to the region. I think you are misreading it if you think there is not a mutual interest.'

Kerry claimed the U.S. has 'the capacity' to 'knock out ISIL' on its own, but 'we're not going to get suckered into that.'

'The enduring transformation that has to take place here is not going to take place if the United States just comes in and were to knock out ISIL and that’s it – go away,' he said, adding that it's 'not gonna happen.'

But Cotton's letter, also signed by Senate Majority Leader Mitch McConnell and several Republican presidential hopefuls, was Exhibit A on Wednesday.

Formal treaties require ratification by two-thirds of the Senate, but 'the vast majority of international arrangements and agreements do not,' Kerry said.

'And around the world today we have all kinds of executive agreements that we deal with,' including 'any number of noncontroversial, broadly supported foreign policy goals.'

START OF IT ALL: Arkansas freshman Senator Tom Cotton wrote a letter to Iran's leaders and persuaded 46 other Republicans in the Senate to sign it with him

The Obama administration and Senate Democrats have harshly condemned Cotton's letter, which was presented to leaders of the Islamic republic as a primer on the U.S. Constitution.

It warned 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.'

As Kerry's turn on the hot seat began, protesters from the liberal anti-war group Code Pink interrupted – as they have done in other recent hearings.

Like Arizona Sen. John McCain, who last month called them 'low-life scum' as they were led out of a hearing room, Kerry fired back at a woman who shouted repeatedly that 'the United States is killing innocent civilians with drones!'

'Killing more innocent people?' he asked aloud. 'I wonder how our journalists, who were beheaded, and a pilot who was fighting for freedom – burned alive – what they would have to say to their efforts to protect innocent people.'

ENEMY OF MY ENEMY: Florida Sen. Marco Rubio heard Kerry say that Iran is helpful in fighting the ISIS terror army

The secretary of state will meet Iran's foreign minister, Mohammad Javad Zarif, next week in Switzerland for another round of talks.

He said Cotton's letter 'erroneously asserts that this is a legally binding plan. It's not, that's number one.'

'Number two, it's incorrect when it says that Congress could actually modify the terms of an agreement at any time. That's flat wrong,' he continued. 'They don't have the right to modify an agreement reached executive to executive between leaders.'

Neither the U.S. nor Iran has emphasized the need for a legally binding deal because each has stronger forms of leverage. If Iran cheats, the Obama administration has spoken of re-imposing suspended sanctions. The U.S. has also held out the prospect of military action if Iran makes progress toward a nuclear weapon.

Similarly, if the U.S. doesn't live up to its side of the bargain, the Iranians can ramp up enrichment levels of uranium, taking them closer to nuclear weapons capacity.

Congress, too, wields a threat: new forms of economic punishment of Iran that would be forbidden in the agreement.

But such a move would almost surely require overriding a presidential veto and could pin any diplomatic collapse on the United States.

Negotiators from the U.S., Britain, China, France, Germany and Russia hope to seal a framework with Iran by month's end and a comprehensive agreement by July.

Kerry scoffed at the notion that Obama's successor would discard a deal reached between so many powerful governments and adhered to by Iran.

'I'd like to see the next president, if all of those countries have said this is good and it's working, turn around and just nullify it on behalf of the United States,' he said. 'That's not going to happen.'

READY TO MAKE HISTORY: Kerry shook hands with new Defense Secretary Ash Carter (left) as protesters anticipated the start of Wednesday's hearing

Questions about the process involved in any agreement with Shiite-majority Iran are sensitive for a variety of reasons.

Israel, Sunni Arab countries and many U.S. lawmakers are concerned that international negotiators could be placing too much trust in Iran.

The prospects of a 'nonbinding' pact will hardly alleviate their concerns, even if none of them have professed faith in Iran abiding by the terms of an agreement that would ease sanctions in exchange for at least a decade of strict limits on the Iranian nuclear program.

Iran says its program is solely for peaceful energy and medical research purposes.

On Tuesday, Jen Psaki, Kerry's spokeswoman, raised the possibility of the deal assuming legal character through the U.N. Security Council.

Psaki didn't speak definitively on the matter but cited the example of a 2013 strategy agreed to between the U.S. and Russia on Syria relinquishing its chemical weapons stockpile. That plan was then endorsed by the United Nations' top body.

'This framework was not legally binding and was not subject to congressional approval,' Psaki told reporters during a daily press briefing.

'It outlined steps for eliminating Syria's chemical weapons and helped lay the groundwork for successful multilateral efforts to move forward.' In that case, she added, the U.S.-Russian agreement 'went to the U.N. to the Security Council vote.'

Zarif is the only one who has gone on record saying such a model would be followed with a nuclear deal.