Senate Republicans plan to dramatically overhaul the House ObamaCare replacement bill that passed Thursday and are warning the process could take weeks.

The House bill, the American Health Care Act, has raised an array of concerns among Senate Republicans, chiefly among lawmakers from swing states who are opposed to the cap on ObamaCare’s Medicaid expansion that would take effect in 2020.

GOP senators are also troubled by analyses that the legislation would significantly cut federal subsidies for people between the ages of 50 and 65, especially in rural areas such as Maine, Montana, Nebraska and North Carolina.

Senate Republican Whip John Cornyn John CornynGOP lawmaker says panel to investigate drug company gaming of patent system Senators grill drug execs over high prices Cornyn less popular than Cruz in Texas: poll MORE (R-Texas) announced Thursday that there would no “arbitrary deadlines” for the healthcare legislation, setting up an open-ended process.

“We’re going through the issues methodically,” he said. “The House passing the bill gives us a little bit more of a sense of urgency, but it’s going to take a while.”

Senate Republicans say the bill in its current form cannot pass, and some of them privately question whether it will ever get a floor vote. There’s also skepticism in the conference that they will be able to cobble together 51 votes behind any plan.

“I think it needs a lot of improvement,” Sen. Shelley Moore Capito Shelley 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 (R-W.Va.), who is concerned about the Medicaid provisions, said about the House bill.

West Virginia has been one of the biggest beneficiaries under ObamaCare’s Medicaid expansion, with 175,000 new people signing up under the law’s more generous guidelines as of 2015.

Capito said she is also worried about the reductions in subsidies for older, less affluent people under the House plan.

For example, a person who is 60 years old earning $30,000 a year in Kanawha County, W.Va., would see a subsidy reduction of nearly $9,000 a year under the House proposal.

Sens. Rob Portman Robert (Rob) Jones PortmanAddressing repair backlog at national parks can give Congress a big win Texas senator introduces bill to produce coin honoring Bushes GOP Green New Deal stunt is a great deal for Democrats MORE (R-Ohio) and Dean Heller Dean Arthur HellerTrump suggests Heller lost reelection bid because he was 'hostile' during 2016 presidential campaign Trump picks ex-oil lobbyist David Bernhardt for Interior secretary Oregon Dem top recipient of 2018 marijuana industry money, study finds MORE (R-Nev.), two Republicans who have sounded the alarm about the potential Medicaid rollback, issued statements Thursday afternoon opposing the House bill.

Portman said he doesn’t support the measure “because I continue to have concerns that this bill does not do enough to protect Ohio’s Medicaid expansion population.”

Portman said on Wednesday that he would like to see “a longer runway” for reforming Medicaid instead of abruptly capping the program two and a half years in the future.

Heller said “the current bill falls short” and “we cannot pull the rug out from under states like Nevada that expanded Medicaid.”

The House bill could also face resistance from some of the Senate’s most conservative members.

Sen. Rand Paul Randal (Rand) Howard PaulWhite House pleads with Senate GOP on emergency declaration The Hill's Morning Report — Emergency declaration to test GOP loyalty to Trump The Hill's 12:30 Report: Trump escalates fight with NY Times MORE (R-Ky.) said that while changes to the legislation insisted on by members of the House Freedom Caucus improved the legislation, he’s still not satisfied.

"I really frankly am not too excited about subsidizing the profit of insurance companies," Paul told Fox News in an interview Thursday.

"There's about $300 or $400 billion in this bill for insurance company profit," he added. "It boggles my mind how that became a Republican idea.”

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellWhite House pleads with Senate GOP on emergency declaration Senate Dems seek to turn tables on GOP in climate change fight Pence meets with Senate GOP for 'robust' discussion on Trump declaration MORE (R-Ky.) cautioned Tuesday that getting a healthcare bill through the Senate would be “a real big challenge.”

He has convened a working group that includes members of his leadership team, moderates who are worried about the Medicaid rollback, conservatives and two key committee chairman — Senate Finance Committee Chairman Orrin Hatch Orrin Grant HatchThe FDA crackdown on dietary supplements is inadequate Orrin Hatch Foundation seeking million in taxpayer money to fund new center in his honor Mitch McConnell has shown the nation his version of power grab MORE (R-Utah) and Senate Health, Education, Labor and Pensions Committee Chairman Lamar Alexander Andrew (Lamar) Lamar AlexanderWhite House pleads with Senate GOP on emergency declaration Overnight Health Care: Senators grill drug execs over high prices | Progressive Dems unveil Medicare for all bill | House Dems to subpoena Trump officials over family separations Schumer urges GOP to reject Trump's 'destructive' national emergency MORE (R-Tenn.) — to work out a compromise.

The group met Tuesday and again on Thursday.

“The majority leader has pulled together a working group of people that represent different approaches, trying to get consensus there, and we’re going through the issues methodically,” Cornyn later told reporters.

Alexander has been working for weeks on a healthcare reform bill that could pass the Senate with only Republican votes.

He has begun working closely with Sen. Ted Cruz Rafael (Ted) Edward CruzCornyn less popular than Cruz in Texas: poll Trump unleashing digital juggernaut ahead of 2020 Inviting Kim Jong Un to Washington MORE (R-Texas), a conservative who earlier this year voiced misgivings about the House healthcare reform bill but who could emerge as the key to getting a deal.

McConnell initially hoped to pass the House healthcare reform bill through the Senate quickly.

He first eyed the last week of March for the job, but the political calculations changed after Speaker Paul Ryan Paul Davis RyanBrexit and exit: A transatlantic comparison Five takeaways from McCabe’s allegations against Trump The Hill's 12:30 Report: Sanders set to shake up 2020 race MORE (R-Wis.) failed to muster enough votes for the legislation on March 24 and pulled it from the floor.

As it’s become increasingly clear how much opposition there is within the Senate to the bill, McConnell has opted for a less ambitious timeline.

Twenty House GOP lawmakers voted against the legislation Thursday, and some of them criticized it in harsh terms.

Rep. Ileana Ros-Lehtinen (R-Fla.) said the bill “has the potential to severely harm the health and lives of people in South Florida.”

McConnell initially planned to bring the House bill directly to the floor, but now he wants to vet it through the working group he has assembled to make sure it can get 51 votes.

Senate Republicans control 52 seats and so can afford only two defections, as Vice President Pence could break a 50-50 tie.

The expected plan is to use the working group instead of the primary committees of jurisdiction, the Finance and Health panels, to negotiate the bill.

“I think what you’re going to see is more of a working group approach, which has already started to meet,” Cornyn said.

But not all Republicans are thrilled about bypassing the committees.

“My hope is that we treat the bill seriously, that we have hearings, that we have witnesses,” said Sen. Jerry Moran Gerald (Jerry) MoranOn The Money: House votes to block Trump emergency declaration | McConnell unsure if Trump move is legal | Fed chief sees 'conflicting signals' from economy | Governors bullish on infrastructure after Trump talks | Big win for AT&T-Time Warner deal Fed chief sees 'conflicting signals' from economy The Hill's Morning Report — Emergency declaration to test GOP loyalty to Trump MORE (R-Kan.). “I want the regular order to work.”

Not a single House Democrat voted for the ObamaCare repeal legislation in the House, and Democratic leaders said Thursday that it would not get any support from their conference in the Senate.

“The proposal that is coming from the House doesn’t have a pulse in terms of Senate Democrats,” said Sen. Ron Wyden Ronald (Ron) Lee WydenTreasury official: Tax withholding guidance wasn't manipulated for political reasons Cohen grilled by Senate Intelligence panel Senate confirms Trump court pick despite missing two 'blue slips' MORE (Ore.), the senior Democrat on the Finance Committee.