By a nearly 2 to 1 margin, Americans support the notion of striking a deal with Iran that restricts the nation’s nuclear program in exchange for loosening sanctions, a new Washington Post-ABC News poll finds.

But the survey — released hours before Tuesday’s negotiating deadline — also finds few Americans are hopeful that such an agreement will be effective. Nearly six in 10 say they are not confident that a deal will prevent Iran from developing nuclear weapons, unchanged from 15 months ago, when the United States, France, Britain, Germany, China and Russia reached an interim agreement with Iran aimed at sealing a long-term deal.

Overall, the poll finds 59 percent support an agreement in which the United States and its negotiating partners lift major economic sanctions in exchange for restrictions on Iran’s nuclear program. Thirty-one percent oppose a deal.

Support outpaces opposition across nearly all demographic and political groups, with liberals (seven in 10) and Democrats (two-thirds) the most supportive. At least six in 10 independents and moderates also back the broad idea of a deal with Iran.

Republicans are about evenly divided on an Iran deal, with 47 percent in support and 43 percent opposed. The split contrasts with Republican lawmakers’ widespread backing of Israeli Prime Minister Benjamin Netanyahu’s speech deriding the potential deal in early March before a joint meeting of lawmakers. Additionally, all but seven Republican senators signed a letter to Iran’s leadership warning that Congress or a future president could override any agreement made by the Obama administration.

Popular sentiment among Republicans is more in line with GOP lawmakers on the issue of whether Congress should be required to authorize any deal with Iran. A Pew Research Center survey released Monday found 62 percent of the public believes Congress, not President Obama, should have final authority over approving a nuclear agreement with Iran.

Republican Sen. Bob Corker (Tenn.), the Senate Foreign Relations Committee chairman, and other lawmakers are building bipartisan support for a bill that would require Obama to submit an Iran agreement for congressional approval blocking the removal of sanctions on the Islamic republic for 60 days. The bill would require a veto-proof majority to force Obama’s hand.

Americans’ views on Iran have been shaped by deep worry over the prospect that it could develop nuclear weapons but also a hesitance to employ military force in an attempt to prevent that outcome. A February Gallup poll found more than three-quarters of the public thinks the development of nuclear weapons by Iran would pose a “critical threat” to the United States over the next 10 years. Yet fewer than three in 10 said Iran’s nuclear program — which it insists is for peaceful purposes — requires military action now in a CBS News poll last week; more than four in 10 said the threat can be contained for now and just under two in 10 said Iran is not currently a threat.

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National telephone polls have found varying support for the notion of a deal with Iran, with surveys surrounding the late 2013 deal ranging from 44 percent to 64 percent support surveying voters or adults.

The latest Post-ABC poll’s 59 percent closely mirrors a February survey by the independent Program for Public Consultation. The survey, which provided respondents with detailed briefings approved by congressional staff from both parties, found 61 percent preferring to make a deal with Iran that allows limited uranium enrichment over ramping up sanctions to push for a complete end to Iran’s nuclear program.

The Post-ABC survey finds that even those with limited hopes of a fruitful agreement are open to a deal. Support crests above 80 percent among respondents who are at least “somewhat” confident a deal will stop Iran from obtaining nuclear weapons. But even among those who are “not so confident” about an agreement succeeding, two in three support a deal. Only among those who are not confident at all about stopping Iran does opposition rise to a majority, though even here, 31 percent support a deal.

While polls find support for Obama’s approach of negotiating toward an agreement, he receives negative marks for dealing with Iran overall. The CBS News poll found 38 percent approving of his handling of relations with Iran, significantly worse than his overall job rating.

The Post-ABC poll was conducted March 26 to 29 among a random national sample of 1,003 adults interviewed by telephone, including 335 cellphone-only respondents. The overall margin of error is plus or minus 3.5 percentage points.

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See: The Washington Post-ABC News poll

Fact-checking Obama’s reference to “unprecedented” nuclear inspections

A framework? A deal? The semantics of the talks.