The more Americans know about the nuclear deal with Iran, the less they seem to like it, according to the latest polls on the issue.

Support for the agreement signed July 14 is declining at a critical time. Lawmakers head home next week for the August recess and will have to face voters' concerns head-on before a September vote on whether to approve or disapprove of it.

Most of those who were polled as talks were going on and a deal was still undefined supported the idea of a peaceful solution to Iran's nuclear ambitions, though most also did not trust Tehran to keep any bargain.

That mistrust of Iran seems to have developed into mistrust of the deal itself since its details were announced. In a Pew Research Center survey of 2,002 adults taken July 14-20, only 38 percent of the 79 percent of those who had heard of the deal approved, while 48 percent disapproved. The margin of error was plus or minus 2.7 percentage points.

A CNN/ORC poll of 1,107 adults taken July 22-25 found that 52 percent wanted Congress to reject the deal. That poll had a margin of error of plus or minus 3 percentage points.

On the other hand, a Washington Post/ABC News poll of 1,002 adults taken July 19 found that 56 percent supported the deal versus 37 percent who opposed it. But 64 percent of respondents also said they were not confident the deal would prevent Iran from developing a nuclear weapon. The margin of error was plus or minus 3.5 percentage points.

The Pew and Post/ABC polls worded their questions significantly differently, which may account for the discrepancy in results. The Pew poll first asked respondents, "How much, if anything, have you heard about a recent agreement on Iran's nuclear program between Iran, the United States and other nations?" and then asked: "From what you know, do you approve or disapprove of this agreement?" The Post/ABC poll asked: "As you may know, the U.S. and other countries have announced a deal to lift economic sanctions against Iran in exchange for Iran agreeing not to produce nuclear weapons. International inspectors would monitor Iran's facilities, and if Iran is caught breaking the agreement economic sanctions would be imposed again. Do you support or oppose this agreement?"

Though most Republicans already have come out against the deal, most Democrats remain undecided, including well-known Iran skeptics such as Rep. Brad Sherman of California, who describes the deal as a combination of "the good, the bad and the ugly."

House Democrats are widely expected to be President Obama's firewall against any disapproval resolution, with Minority Leader Nancy Pelosi, D-Calif., saying Thursday she has enough votes to sustain a veto.

But questions about the deal are causing support to erode among lawmakers as well, and if current poll trends continue, public distrust could sway more defections.

A day after Tuesday's House Foreign Affairs Committee hearing on the deal with Secretary of State John Kerry, Energy Secretary Ernest Moniz and Treasury Secretary Jack Lew, committee member Grace Meng, D-N.Y., came out against it, saying she wants a more favorable arrangement.

"I commend President Obama and Secretary Kerry for their efforts to prevent Iran from acquiring a nuclear weapon, but the deal before us now is simply too dangerous for the American people. I have every confidence a better deal can be realized," she said.