WASHINGTON (AP) — Oregon's Democratic Sen. Jeff Merkley has become the 31st senator to announce support for the Iran nuclear deal, as momentum builds behind the agreement the Obama administration and other world powers negotiated with Tehran.

Merkley's backing on Sunday puts supporters within reach of the 34 votes required to uphold a presidential veto of a congressional resolution disapproving the agreement.

Republicans are unanimously against the deal, which provides sanctions relief to Iran in exchange for constraints on its nuclear program.

But with an overwhelming number of Senate Democrats in favor, some supporters have now begun aiming to amass 41 yes votes.

Forty-one votes in favor would allow Democrats to kill the disapproval resolution outright in the Senate, making it unnecessary for Obama to use his veto pen.