Several Republican senators sent a warning shot to the House after its passage of an ObamaCare repeal-and-replace bill Thursday, indicating it won’t be easy to get the measure through the upper chamber.

Sen. Dean Heller Dean Arthur HellerOn The Trail: Democrats plan to hammer Trump on Social Security, Medicare Lobbying World Democrats spend big to put Senate in play MORE (R-Nev.), one of the most vulnerable GOP senators up for reelection in 2018, said he wouldn’t support the House’s bill in its current form.

“We cannot pull the rug out from under states like Nevada that expanded Medicaid and we need assurances that people with pre-existing conditions will be protected,” he said in a statement.

ADVERTISEMENT

Sen. Rob Portman Robert (Rob) Jones PortmanRomney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery House passes B bill to boost Postal Service MORE (R-Ohio) made clear his concerns over how the House bill treats Medicaid. While ObamaCare expanded the healthcare program to more low-income Americans, the House bill would eliminate that expansion in 2020.

“I’ve already made clear that I don’t support the House bill as currently constructed,” Portman said in a statement, “because I continue to have concerns that this bill does not do enough to protect Ohio's Medicaid expansion population, especially those who are receiving treatment for heroin and prescription drug abuse.”

Republicans have little margin for error in the Senate. With a 52-48 majority, they can only afford to lose two votes — assuming Vice President Pence swoops in to break a tie — under the fast-track budget maneuver Republicans are using to repeal ObamaCare.

Sen. Lamar Alexander Andrew (Lamar) Lamar AlexanderTrump health officials grilled over reports of politics in COVID-19 response Now is the time to renew our focus on students and their futures CDC says asymptomatic people don't need testing, draws criticism from experts MORE (R-Tenn.) pointed to the difficulties to come. He highlighted his three priorities for the bill, which include rescuing Americans in areas where their health marketplaces may not have any insurers offering plans in 2018.

“The Senate will now finish work on our bill, but will take the time to get it right,” Alexander, chairman of the Senate Health, Education, Labor and Pensions Committee, said in a statement.

ADVERTISEMENT

The House passed the American Health Care Act in a 217 to 213 vote, sending the bill to the upper chamber. Yet, Senate leadership has acknowledged the legislation will need to change in the chamber in order to get enough of its members on board.

“We can’t be for half a dozen different proposals; we have to be for a proposal for us to get 51 votes in the Senate,” Senate Majority Whip John Cornyn John CornynSenate Republicans signal openness to working with Biden Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Republican Senators raise concerns over Oracle-TikTok deal MORE (R-Texas) told The Hill an hour before the House vote.

“We’ll start with the House bill, but we’ll need to work with every member of the Senate conference to see what they need to get to yes.”

Likely changes could focus on Medicaid and adding increased financial assistance, in the form of tax credits, to help low-income Americans afford health insurance.

It’s possible the Senate could run into the same problem the House toiled over for almost two months. Move the bill to right, and moderates will defect. Move the bill to the center, and the measure will lose conservative votes.

ADVERTISEMENT

An eleventh-hour amendment to the House bill from Rep. Fred Upton (R-Mich.) — a former chair of the House Energy and Commerce Committee who came out against the bill earlier this week — helped secure the support of enough House moderates to pass the bill.

The amendment provided $8 billion over five years to help people with pre-existing conditions afford premiums in states that opt out of a core ObamaCare provision banning health insurers from charging consumers more based on their health.

The House voted on the bill without a new score from the nonpartisan Congressional Budget Office, which drew the ire of some lawmakers. Rep. Mike Coffman (R-Colo.) cited the lack of a CBO score as one of the main reasons why he voted against the bill.

And Sen. Lindsey Graham Lindsey Olin GrahamSenate Republicans signal openness to working with Biden Loeffler calls for hearing in wake of Netflix's 'Cuties' Quinnipiac poll shows Graham, Harrison tied in South Carolina Senate race MORE (R-S.C.) tweeted that “A bill — finalized yesterday, has not been scored, amendments not allowed, and 3 hours final debate — should be viewed with caution.”