The Oregon Democratic senator Jeff Merkley on Sunday became the 31st senator to announce support for the Iran nuclear deal, as momentum continued to build behind the agreement the Obama administration and other world powers negotiated with Tehran.

Merkley’s backing put supporters within reach of the 34 votes required to uphold a presidential veto of a congressional resolution disapproving the agreement, which curbs Iran’s nuclear program in exchange for billions of dollars in sanctions relief.

Republicans, who control the Senate, are unanimously against the deal. But with an overwhelming number of Senate Democrats in favor, some have now begun aiming to amass 41 yes votes, which would allow them to kill the disapproval resolution outright in the Senate and protect Obama from having to use his veto pen.

A vote on the nuclear deal the US and five other world powers negotiated with Iran is scheduled for early September.

Merkley said that while he thinks the deal has “significant shortcomings”, it is the best strategy to block Iran from acquiring a nuclear weapon.

“Because of these shortcomings, many have argued that the United States, instead of implementing the agreement, should withdraw from it, persuade our partners to set the agreement aside and work together to negotiate a better deal,” Merkley said in a statement.

“However, the prospects for this are slim. All of our partners … believe that the current deal – in regard to its central goal of blocking Iran’s pathways to a nuclear bomb – is sound.

“They have committed the good faith of their governments behind the agreement and intend to honor the deal as long as Iran does likewise, with or without the United States.”