President Barack Obama will present the Iran nuclear debate as the most momentous US foreign policy decision since the Iraq war Wednesday, in a fresh bid for support.
With the deal due to be voted on by a Republican-dominated Congress, Obama will give an address at American University in Washington hoping to give historical weight to a polarizing and sometimes bitterly hyperbolic debate.
The speech will take place at 11:20 local time (1520 GMT).
He will frame lawmakers' decision as "the most consequential" since Congress in 2002 backed George W. Bush's war with Iraq, according to a White House official.
Obama has long argued that the Iraq vote represented a grave mistake that pushed the United States into eight blood-soaked years of unnecessary conflict.
- Kennedy parallels -
"He will point out that the same people who supported war in Iraq are opposing diplomacy with Iran, and that it would be an historic mistake to squander this opportunity," the official said.
Positing the unpopular Iraq war as a cautionary tale, Obama is likely to recall president John F. Kennedy's diplomatic efforts to curb nuclear tests as a more worthy example to follow.
In a 1963 commencement address, Kennedy used the same university venue to argue vehemently for peace with the Soviet Union in the face of panic over a nuclear conflagration.
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Speaking just months before his assassination, Kennedy cautioned against brandishing US power to bring about a the "peace of the grave or the security of the slave."
Instead, he announced diplomatic efforts to check "one of the greatest hazards which man faces in 1963, the further spread of nuclear arms."
Obama's diplomatic deal would give Iran sanctions relief in exchange for curbs on its nuclear program, which Washington long believed was cover for building a bomb.
Obama has argued that the only alternative to negotiations with Iran is military action, something his critics angrily denounce as a false dichotomy.
The alternative to a bad deal, they say, is a better deal that not just subjects Iran to inspections and limits enrichment, but dismantles the nuclear program altogether.
The debate has split Congress largely -- although not exclusively -- along party lines, with Republicans, who are in the majority, staunchly against the accord.
Obama will need to win the support of fellow Democrats in order to avoid having the deal struck down by lawmakers.
Here, history may prove as much a burden as an aid to Obama.
The United States and Iran severed ties following the 1979 Islamic Revolution, which saw 52 American embassy staff and citizens held hostage for 444 days.
Iran's antagonism toward the United States, Israel and support for terror groups in the Middle East since then has given many lawmakers pause, with a number of Democrats already breaking ranks.