His approval rating may have sunk to a new low, right there with the portion of cooperative spirit left in the Republican ranks, but President Barack Obama is gambling that he can somehow reverse a searing, if low-profile, loss from a year ago on a proposal with global implications and domestic political import.

The pact, to which 138 other countries have committed, is written with the principal goal of extending around the word a system of accommodations very similar to what’s spelled out for this country in the Americans with Disabilities Act. That law, passed 23 years ago with overwhelming majorities of Republicans and Democrats alike, stands as the most recent important new civil rights law enacted with genuinely expansive bipartisan backing, and public support for it remains strong.

Obama is betting he can resurrect just enough of that that cross-party spirit to score an upset victory for the treaty on his second attempt. His team has not yet revealed what tactics he has up his sleeve to get there, but for two reasons it’s understandable why he’s trying.

His standing as a global moral authority continues to be tested as he moves toward the final quarter of his tenure, when many second-term presidents turn to international affairs as a way to bolster their legacies. An overhaul of the voting rights law is stuck at the starting gate and a proposed ban on workplace bias against gays and lesbians is on a high shelf in the House, but bringing the ADA’s benefits to people overseas may be one of Obama’s last chances to win something for victims of discrimination.

Advocates argue that international acceptance of the ADA’s precepts — principally, that public buildings be accessible to the physically disabled and that the disabled should be legally protected from workplace bias — would benefit millions of Americans who now find it impossible to work, study or vacation in much of the world. And since a federal law is the basis for the U.N. treaty, proponents say ratification would change almost nothing about life in the United States.

Opponents don’t see it that way at all. Beyond the default arguments the conservatives mount against most foreign treaties — they will hamper American sovereignty and give rise to frivolous litigation — the right has focused in on two narrow arguments. First, compliance would put government officials, not parents, in charge of deciding whether homeschooling is the best course for disabled children. And second, that ratification would lead to more abortions because the treaty guarantees the disabled equal access to reproductive health services.

The United Nations convention was rejected last December, when only eight Republican voted for it. Given that treaties require two-thirds majorities for ratification, and that there are 55 senators in the all-on-board Democratic caucus, that means Obama needs to find a dozen GOP supporters this time.

It’s not an insurmountably tall order.

Five of the Senate Republicans who voted “yes” then remain now: Kelly Ayotte of New Hampshire, John Barrasso of Wyoming, Susan Collins of Maine, John McCain of Arizona and Lisa Murkowski of Alaska.

Another vote is assured from Mark S. Kirk of Illinois, who a year ago was still recovering from a stoke that has made him, in his words, “a recently disabled American.”

Thad Cochran, who is weeks away from announcing whether he’ll retire or seek a seventh term in Mississippi, switched from “yes” to “no” during the 2012 roll call, once it became clear the treaty was doomed to rejection either way.

Bob Corker, the senior Republican on theForeign Relations Committee, has signaled that he’s moved into the undecided column this time. His eventual “yes” vote could help persuade Tennessee’s other sometimes-centrist GOP senator, Lamar Alexander, to make a similar switch.

A full-throated endorsement from McCain might similarly provide some cover to his iconoclastic buddy Lindsey Graham of South Carolina, or to Arizona’s other senator, freshman Jeff Flake.

Flake was among the 10 GOP senators who voted this month for the Employment Non-Discrimination Act, the measure banning job discrimination on the basis of sexual orientation and gender identity. Others on that list eyed as potentially persuadable on the disabilities treaty include Rob Portman of Ohio and Dean Heller of Nevada.

McCain is one of three former GOP presidential nominees in favor of the treaty, along with President George Bush and the party’s 1996 standard-bearer, former Senate Majority Leader Bob Dole. (A second former GOP leader, Bill Frist of Tennessee, has also publicly endorsed the accord.)

Dole, who lost the use of his right arm in World War II and now uses a wheelchair, shone a national spotlight on the treaty’s rejection by appearing on the floor and beseeching some fellow centrist Republicans to belatedly change their minds. That dramatic moment didn’t turn the tide then, but advocates say the 90-year-old Dole’s efforts helped shape their targeting list this time.

Fellow Kansan Jerry Moran, for example, was among the final GOP holdouts then, and advocates see him as persuadable to reverse course this time.

Administration officials say their lobbying push is much more sustained than last time, with U.N. Ambassador Samantha Power coordinating the effort and leading it with a series of visits to senators’ officers. Disabled advocates, religious organizations and several associations of corporate leaders are also more engaged this time, and are forcefully moving to rebut the arguments about home schooling and abortions.

On unimpeachable argument on their side: December may offer some thin gruel legislatively, but the days in session aren’t a lame duck. A year ago, 36 GOP senators declared, as their only reason for opposing the treaty, that such post-election sessions were an inappropriate venue for treaty deliberations.