(Bloomberg) -- Senate Republicans gave up on their last-ditch proposal to repeal Obamacare Tuesday as opposition in their own ranks ended months of fruitless efforts to gut the Affordable Care Act.

"We don’t have the votes," bill co-sponsor Bill Cassidy of Louisiana told reporters in Washington. "We’ve made the decision, since we don’t have the votes, we’ll postpone that vote."

The chamber won’t vote before Saturday’s deadline to use a fast-track procedure to keep Democrats from blocking a GOP-only bill. On Monday, Republican Senator Susan Collins of Maine added her opposition to that of GOP Senators John McCain of Arizona and Rand Paul of Kentucky, enough to sink the legislation in the 52-48 Senate.

"It’s only a matter of when" the measure will be enacted, said co-sponsor Lindsey Graham of South Carolina. "We’re coming back to this after taxes." Senate Republicans plan next to work on legislation to overhaul the U.S. tax system.

Republicans have campaigned on repealing Obamacare for seven years, and they thought their goal was in sight when the GOP took control of the presidency as well as both houses of Congress in January. While House Republicans passed a bill in May and celebrated at the White House Rose Garden with President Donald Trump, their measure wasn’t acceptable to the Senate, which has been unable to agree on a plan of its own.

Senate Majority Leader Mitch McConnell’s own proposal stumbled to an embarrassing 49-51 defeat in July, with McCain providing the final "no" vote. The House and Senate proposals were crafted in secret, with no public hearings or input from Democrats.

Trump has repeatedly criticized congressional Republicans for failing to quickly send a repeal bill to his desk after promising for seven years to end the Affordable Care Act. Republicans could revive efforts to repeal Obamacare in the next fiscal year starting Oct. 1, though it would be much more difficult to do as their primary focus will be on overhauling the U.S. tax system.

The Graham-Cassidy proposal would turn Obamacare funds into block grants for the states and cut Medicaid funds to states that expanded the program under the Affordable Care Act. It would leave most of the Obamacare taxes in place.