The Strategic Arms Reduction Treaty cleared a key hurdle Saturday when Democrats easily beat back a GOP amendment to the agreement’s preamble designed to scuttle the treaty.

Democrats defeated the amendment on a 59-37 vote. Foreign Affairs ranking member Dick Lugar (Ind.) and Sens. Bob Bennett (Utah) and George Voinovich (Ohio) broke with their GOP colleagues in voting against the amendment. Sen. Joe Lieberman (I-Conn.) broke with the Democratic Caucus and voted for the change.

The amendment, offered by Sens. John McCain (Ariz.) and John Barrasso (Wyo.), was ostensibly designed to remove preamble language linking offensive and defensive missile systems. But because it would directly change the language of the treaty, it would have had the effect of killing the agreement.

Republicans have complained that the deal will constrain the nation’s ability to develop missile defense systems, and that the changes are needed to protect the nation. But in a letter to Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) on Saturday, President Barack Obama dismissed those complaints.

“Regardless of Russia’s actions in this regard, as long as I am president, and as long as the Congress provides the necessary funding, the United States will continue to develop and deploy effective missile defenses to protect the United States, our deployed forces, and our allies and partners,” Obama said in the letter.

Following the vote, Reid announced the Senate would resume work on START on Sunday, beginning at noon. Votes on three GOP amendments are expected to begin at 2 p.m. Those amendments include a proposal by Sen. James Risch (Idaho) to modify the treaty’s preamble, a measure similar to the failed McCain amendment.