Republican Sens. Shelley Moore CapitoShelley Wellons Moore CapitoDems slam EPA plan for fighting drinking water contaminants GOP senator: Border deal is 'a very good compromise' Push to include contractor back pay in funding deal hits GOP roadblock MORE (W.Va.) and Susan CollinsSusan Margaret CollinsTexas GOP rep opposes Trump’s use of national emergency to get border wall GOP Sen. Collins says she'll back resolution to block Trump's emergency declaration Talk grows that Trump will fire Dan Coats MORE (Maine) said on Tuesday that they will not support moving forward with the plan to repeal ObamaCare with a delayed replacement.

"My position on this issue is driven by its impact on West Virginians. With that in mind, I cannot vote to repeal ObamaCare without a replacement plan that addresses my concerns and the needs of West Virginians," Capito said in a statement.

Collins said that she is still a "no" on proceeding to the House-passed bill, which would be used as a vehicle for any Senate action.

“We can’t just hope that we will pass a replacement within the next two years. Repealing without a replacement would create great uncertainty for individuals who rely on the [Affordable Care Act] and cause further turmoil in the insurance markets," she said.

She added that she's recommended Sen. Lamar AlexanderAndrew (Lamar) Lamar AlexanderGOP Sen. Collins says she'll back resolution to block Trump's emergency declaration The Hill's 12:30 Report: Trump escalates fight with NY Times The 10 GOP senators who may break with Trump on emergency MORE (R-Tenn.), the chairman of the Senate's Heath, Education, Labor and Pensions Committee, "begin to hold hearings to examine ways to fix the many flaws in the ACA so that it will work better for all Americans.”

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The announcements effectively put the healthcare push in limbo. With a 52-seat majority, Senate Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellFox News has covered Ocasio-Cortez more than any 2020 Dem besides Warren: analysis Durbin after reading Green New Deal: 'What in the heck is this?' Dems think they're beating Trump in emergency declaration battle MORE (R-Ky.) can only afford to lose two senators and still let Vice President Pence break a tie.

Sen. John McCainJohn Sidney McCainMellman: Where are good faith and integrity? GOP senator says Republicans didn't control Senate when they held majority Pence met with silence after mentioning Trump in Munich speech MORE (R-Ariz.) is in Arizona this week recovering from surgery, so McConnell will not have 50 votes until he returns.

If another GOP senator comes out against moving to the bill, McCain's presence will not save it.

Sen. Rob PortmanRobert (Rob) Jones PortmanTexas senator introduces bill to produce coin honoring Bushes GOP Green New Deal stunt is a great deal for Democrats Steel lobby's PR blitz can't paper over damaging effects of tariffs MORE (R-Ohio) said early Tuesday he would need to review the bill, but told reporters that a repeal-only bill "will add to more uncertainty." 

Other senators who balked at the last version of the healthcare bill say they will support moving to the repeal-only bill.

Sen. Jerry MoranGerald (Jerry) MoranThe Hill's 12:30 Report: Trump escalates fight with NY Times The 10 GOP senators who may break with Trump on emergency Senators optimistic about reaching funding deal MORE (R-Kan.), who announced his opposition to the repeal-and-replace bill Monday night, said he would support taking up the House-passed legislation.

"I support the President’s efforts to repeal ObamaCare, and I will vote in favor of the motion to proceed. This should be followed by an open legislative process to craft healthcare policy that will provide greater personal choice, protections for pre-existing conditions, increased access and lower overall costs for Kansans," Moran said.

McConnell is doubling down on the new strategy after he announced on Monday night that the Senate would try to separate ObamaCare repeal and replacement amid growing pressure from President Trump and conservatives.

"I believe we must continue to push forward now. I regret that the effort to repeal and immediately replace the failures of ObamaCare will not be successful. That doesn't mean we should give up," he said from the Senate floor on Tuesday.

The 2015 ObamaCare repeal bill passed the Senate 52-47, with Collins and then-Sen. Mark KirkMark Steven KirkThe global reality behind 'local' problems Dems vow swift action on gun reform next year This week: Trump heads to Capitol Hill MORE (Ill.) the only Republicans to oppose it.

Capito, who previously voted for the 2015 repeal bill, added on Tuesday that she has concerns about what would happen to her state's Medicaid expansion and combating opioid addiction.

"All of the Senate healthcare discussion drafts have failed to address these concerns adequately," the West Virginia senator said.

The 2015 measure guts ObamaCare by repealing authority for the federal government to run healthcare exchanges and scrapping subsidies to help people afford plans bought through those exchanges. It zeros out the penalties on individuals who do not buy insurance and employers who do not offer health insurance.

Crucially for moderate senators, the bill would end ObamaCare's Medicaid expansion in two years.

The Senate is expected to be in session until August 11, when members will leave town until early September.

Conservatives and Trump are pressuring GOP senators to back the legislation, noting most of them supported the measure in 2015 when they knew then-President Obama would veto it.

"I don’t see how any Republican senator who voted just 18 months ago for this very piece of legislation could now flip-flop 18 months on with ObamaCare still inflicting so much harm on Americans, and the fact that we campaigned on this for four straight elections," Sen. Tom CottonThomas (Tom) Bryant CottonSenate approves border bill that prevents shutdown 'Morning Joe' host quizzes Howard Schultz on price of a box of Cheerios Huawei charges escalate Trump fight with China MORE (R-Ark.) told conservative radio host Hugh Hewitt on Tuesday.

But several GOP senators voiced concerns earlier this year about repealing ObamaCare without a replacement plan hashed out.

Portman, Collins, and GOP Sens. Bob CorkerRobert (Bob) Phillips CorkerSasse’s jabs at Trump spark talk of primary challenger RNC votes to give Trump 'undivided support' ahead of 2020 Sen. Risch has unique chance to guide Trump on foreign policy MORE (Tenn.), Bill Cassidy (La.) and Lisa MurkowskiLisa Ann MurkowskiGOP Sen. Collins says she'll back resolution to block Trump's emergency declaration The Hill's 12:30 Report: Trump escalates fight with NY Times The 10 GOP senators who may break with Trump on emergency MORE (Alaska) urged leadership for more time to come up with a repeal plan earlier this year.

GOP leadership initially wanted to pass a repeal-only bill but backtracked over a lack of support. GOP Sen. John ThuneJohn Randolph ThunePolls: Hiking estate tax less popular than taxing mega wealth, income Will Trump sign the border deal? Here's what we know Key GOP senator pitches Trump: Funding deal a 'down payment' on wall MORE (R-S.D.) acknowledged on Tuesday that they could still fall short.

"We’ll now have to go through the exercise of sort of re-whipping this, because we are using live ammunition. You know, when we had this 18 months ago in 2015, we had a Democrat president that everybody knew would veto the bill," he told Hugh Hewitt.

Repealing portions of ObamaCare without enacting a replacement could leave 18 million people without health insurance the following year, according to a report released Congressional Budget Office (CBO) in January.

After the elimination of ObamaCare's Medicaid expansion and insurance subsidies, 27 million people would lose insurance, and then 32 million by 2026, the CBO found.

- This story was updated at 11:47 a.m.