– Momentum continued to build for the Iran nuclear deal Sunday with backing from Republican former Secretary of State Colin Powell, just as Congress prepares to begin a debate likely to end with a highly partisan vote.

The Republicans who control Congress almost unanimously oppose the accord, which was negotiated by the White House and diplomats from other leading nations to curtail Iran’s nuclear ambitions. But with a large majority of Democrats supporting it, President Obama is all but assured of the votes to prevent opponents from blocking it.

Another top Democrat, Rep. Debbie Wasserman Schultz of Florida, the party’s chairwoman, announced Sunday that she would back the deal. Her support is significant because she represents a Florida district with many Jewish voters who worry about the threat Iran poses to Israel. The Israeli government has been a leading force in opposition.

Although a number of House Democrats have not yet declared their position, Democratic leader Nancy Pelosi has said she is confident of having the votes to sustain the deal. Democrats already have enough support on record to do so in the Senate.

Explaining the details of the deal on NBC’s “Meet the Press,” Powell said it would slow Iran’s march toward developing the components needed to build a bomb.

“We have stopped this highway race that we were going down, and I think that’s very, very important,” Powell said.

“Even if we were to kill this deal, which is not going to happen, it would take effect anyway, because all of these other countries that were in it with us are going to move forward,” Powell said. Five other nations — Britain, Germany, France, Russia and China — are aligned with the U.S.

Wasserman Schultz, who is Jewish, said she had struggled with her decision.

“There’s nothing more important to me as a Jew to ensure Israel’s existence,” she said on CNN. “It is the homeland of my people.”