A majority of Americans support the Iran deal despite widespread doubts it will stop the country from developing nuclear weapons, according to new Washington Post-ABC News poll.

The survey finds 56 percent support and 37 percent oppose a deal lifting economic sanctions against Iran in exchange for the nation agreeing not to produce nuclear weapons. Support for the final deal is narrower than for the framework agreement announced in March which received nearly 2 to 1 support in a Post-ABC poll, 59 to 31 percent.

The finalization of the Iran deal has not buoyed confidence that it will work, however. More than six in 10 Americans say they are "not so" or "not at all" confident that the deal will stop Iran from getting a nuclear weapon, up slightly since March. Only 6 percent are "very confident" in the deal's long term success.

Americans also continue to rate Obama negatively for his handling of Iran generally, with 35 percent approving and 52 percent disapproving. Eight in 10 Republicans and 56 percent of independents give Obama negative marks, while a tepid 59 percent of Democrats approve of his efforts. More than one-third of the deal's supporters nevertheless disapprove of Obama's performance on the issue.

President Obama took questions on the deal with Iran in the East Room of the White House on July 15. Here are key moments from that speech. (AP)

Americans appear ready to gamble
Americans are clearly of two minds on Iran, preferring diplomatic efforts to stop the country from developing a nuclear weapon but also expressing deep distrust that Iran can be trusted to abide by any agreement. Thus the public opinion conundrum; 64 percent are not confident the deal will work, yet 56 percent support the agreement.

How to explain it?

First, start with those who do think it will work -- the 35 percent who are "very" or "somewhat" confident the deal will prevent Iran from developing nuclear weapons. Among this group, 86 percent support the deal. This is notable, but it's not enough to sustain majority support.

The key group are the one-fifth of the public who is "not so confident" a deal will work (22 percent). This group supports a deal by a more than 3 to 1 margin (69 to 21 percent), similar to their margin of support for the framework in March.

Support only drops below a majority among those who are "not at all" confident a deal will work (42 percent of the public). Among this group, nearly 7 in 10 oppose the deal (69 percent). The size of this group has grown by eight percentage points since March and is also more unified in its opposition, suggesting the potential for overall support for the agreement to shift going forward.

Republicans surprisingly supportive, but partisan differences are growing
Every Republican U.S. Senator is leaning toward voting "no" on the Iran deal according to the Post's Amber Phillips. But Republicans at-large are a key reason for the deal's continued popularity. The Post-ABC poll found more than 4 in 10 Republicans support the agreement (41 percent), while 54 percent are opposed. Even among conservative Republicans, one-third support a deal with Iran trading economic sanctions for a strict inspection regime.

Democrats are far more united, backing a deal by a 69 to 25 percent margin.

But it's not clear whether GOP support will persist despite public criticism from Congress and presidential hopefuls who criticize the accord as a weak deal. Current support for the deal is slightly more negative than for the framework deal in March, which 47 percent of Republicans supported and 43 opposed.

The Post-ABC poll was conducted July 16-19 among a random national sample of 1,002 adults, including landline and cell phone respondents. Overall results have a margin of sampling error  of plus or minus 3.5 percentage points. Full results of the poll and detailed methodology are available here.

Peyton M. Craighill contributed to this report.

Read more: Obama starts out ahead on the Iran deal. It might not last.