As President Barack Obama prepares to celebrate a diplomatic victory when Congress votes on the Iran nuclear agreement, a new poll showed US public support for the deal has declined.

Only 21% approve of the agreement on Iran’s nuclear program reached between the United States, Iran and five other nations, according to a Pew Research Center poll. Almost half of Americans (49%) disapprove of the deal, while 30% offer no opinion.

In mid-July, a week after President Obama announced the deal, 33% of the public approved of it, while 45% disapproved and 22% had no opinion. Since then, the portion approving of the agreement has fallen 12 percentage points, from 33% to 21%, while disapproval has increased slightly.

The latest national survey by Pew, conducted Sept. 3-7 among 1,004 adults, found that the public is not very preoccupied with the issue. In fact, the share saying they have heard either a lot or a little about the agreement declined from 79% in July to 69% in the new survey, whereas the share saying they have heard “nothing at all” about it has increased from 21% to 30%.

Republicans are far more likely than Democrats or independents to say they have heard about the agreement. Today, 86% of Republicans, 69% of Democrats and 63% of independents have heard at least a little about the nuclear agreement.

Support for the deal has slipped across the political spectrum since July. The share of Democrats who approve of the agreement dropped from 50% in Julay to 425 at present.

Republican support for the agreement, already low, has dropped even further (from 13% to 6%). Independents’ support for the agreement also has fallen (from 31% to 20%).