The Senate’s defeat of an international treaty aimed at eliminating international discrimination against people with disabilities saw Iowa’s two senators split their votes Tuesday.

Sen. Chuck Grassley, R-Iowa, joined 37 other Republicans to vote against the treaty, enough to leave the measure five votes short of passage. Sen. Tom Harkin, D-Iowa, joined 60 others, including eight Republicans, in voting for it.

The treaty, which was negotiated during President George W. Bush’s administration and signed in 2009 by President Barack Obama, has taken on opposition by anti-abortion groups, along with advocates for people who home-school their children and others who argue the measure encourages abortion overseas and impinges on the rights of American parents to educate their children at home.

Conservatives, including former GOP presidential hopeful Rick Santorum, have pushed for its defeat.

Proponents say the treaty is just common sense and has the backing of major disability groups. They say the critics’ claims are fictitious and the treaty would simply move other countries closer to U.S. laws, such as the Americans with Disabilities Act. They say it also would protect Americans overseas.

Former Senate Majority Leader Bob Dole, a longtime advocate for people with disabilities, returned to the Senate on Tuesday to back the treaty.

In the midst of the contentious fiscal-cliff talks, the vote is but another symbol of a polarized Washington, D.C.

Harkin called the vote a “shameful day in our history.”

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Grassley said the United States is a leader in disability rights and it requires no treaty to continue in that vein. He said he’s sponsored legislation that has benefitted people with disabilities, but this treaty made unnecessary references to “sexual and reproductive health” and the “best interests of the child.”

“These provisions call into question the purpose of the convention regarding abortion rights and the fundamental rights of parents to determine how best to raise their children,” he said. He and other Republicans also had sent a letter urging that no treaties be taken up during the lame-duck session.

Proponents said there was no evidence to suggest an impact on U.S. sovereignty, and they disputed that it would encourage abortion or affect parents’ ability to raise their children. Harkin has spoken of the disabled overseas being kept in deplorable conditions and in isolation. The treaty, he said, would give Americans, particularly those with disabilities, a seat at the international table from which they could influence other countries.

“We are the best in the world at this,” said Harkin, the primary author of the Americans with Disabilities Act. “This treaty will make us a better world in which to live.”

Sen. Dick Durbin, D-Ill., also voted for the treaty’s passage.