WASHINGTON (AP) — Top Senate Republicans say their last-ditch push to uproot former President Barack Obama's health care law is gaining momentum. But they have less than two weeks to succeed and face a tough fight to win enough GOP support to reverse the summer's self-inflicted defeat on the party's high-priority issue.

"We feel pretty good about it," Sen. Bill Cassidy, R-La., a leader of the effort along with Sen. Lindsey Graham, R-S.C., said Monday.

"He's the grave robber," No. 3 Senate GOP leader John Thune of South Dakota said of Cassidy. "This thing was six feet under" but now has "a lot of very positive buzz," Thune said.

The 140-page bill would replace much of Obama's law with block grants to states, giving them wide leeway on spending the money, and would cut and reshape Medicaid. It would let states set their own coverage health requirements, allow insurers to boost premiums on people with serious medical conditions and end Obama's mandates that most Americans buy insurance and that companies offer coverage to workers.

With Democrats unanimously against the bill, Republicans commanding the Senate 52-48 would lose if just three GOP senators are opposed. That proved a bridge too far in July, when three attempts to pass similar measures fell short and delivered an embarrassing defeat to President Donald Trump and Senate Majority Leader Mitch McConnell, R-Ky.

McConnell said he'd not bring another alternative to the Senate floor unless he knew he had the 50 votes needed. Vice President Mike Pence would cast the tie-breaking vote. On Tuesday, Pence planned to briefly leave his United Nations meetings in New York to attend the Senate Republican policy lunch in Washington, and then return to the U.N. later in the day.

For Senate Republican leaders, a victory would allow them to claim redemption on their "repeal and replace" effort. The House approved its version of the bill in May.

Democrats backed by doctors, hospitals, and patients' groups mustered an all-out effort to smother the GOP drive, warning of millions losing coverage and others facing skimpier policies. Sixteen patients groups including the American Heart Association and the March of Dimes said they opposed it, as did the American College of Physicians and the Children's Hospital Association.

Potentially complicating the GOP drive, the Congressional Budget Office said it won't have crucial estimates on the bill's impact on coverage ready for several weeks.

Special procedures protecting the GOP bill from filibusters — which take 60 votes to block — expire Sept. 30, and after that Democratic opposition would guarantee its defeat. Some wavering Republican senators could want the nonpartisan budget office's analysis before feeling comfortable about the measure's impact back home.

All but daring Republicans to vote without the budget office figures, Senate Minority Leader Chuck Schumer, D-N.Y., said voting without that information would be "legislative malpractice at the highest."

The budget agency's evaluations of past GOP repeal plans concluded they would have caused millions of Americans to lose insurance coverage.

Pence was calling senators to seek support, White House officials said. House Speaker Paul Ryan, R-Wis., said the House would vote on the bill if it passes the Senate. Speaking in Menomonee Falls, Wisconsin, Ryan called it "our best, last chance to get repeal and replace done."

The bill would reduce spending gaps between states that expanded Medicaid under Obama's law and the mostly GOP states that did not. Details on the measure's exact state-by-state impact were murky.

Conservative Sen. Rand Paul, R-Ky., has said he'll oppose the measure because it doesn't do enough to erase Obama's law. Sen. Susan Collins, R-Maine, said she was concerned the bill would make "fundamental changes" in Medicaid.

Other Republicans who've not yet lined up behind the bill include Alaska's Lisa Murkowski, Shelley Moore Capito of West Virginia, John McCain of Arizona and Ohio's Rob Portman.

Collins, Murkowski and McCain provided the decisive votes against the last measure Republicans tried to push through the Senate in July.

"It's better but it's not what the Senate is supposed to be doing," McCain told reporters about the new package.

Arizona GOP Gov. Doug Ducey said he backed the new bill, putting pressure on McCain.

The revived drive comes as Sens. Lamar Alexander, R-Tenn., and Patty Murray, D-Wash., work toward a bipartisan deal to continue federal subsidies to insurers that are used to ease some costs for lower-earning customers. Trump has threatened to block the subsidies.

Murray spokeswoman Helen Hare said Murray is "hopeful and optimistic" a deal could come soon, a statement that came as Democrats tried peeling away GOP support from the Graham-Cassidy bill.

Associated Press writers Kevin Freking, Andrew Taylor and Richard Lardner in Washington and Scott Bauer in Menomonee Falls, Wisconsin, contributed to this report.