The House of Representatives has narrowly passed a budget resolution intended to repeal a number of core tenets of the 2010 Affordable Care Act, with 20 Republicans voting against the bill. It now heads on to the Senate, where the GOP can’t really afford to have any of its members voting no. However, a number of Republicans have already expressed skepticism of what’s in the legislation.

Because the GOP’s American Health Care Act is technically a budget resolution, it only requires a simple majority in the Senate to pass. Republicans have 52 of the 100 seats in the Senate, so only two party members could break ranks; a 50-50 tie vote would be broken by Vice President Mike Pence, who supports the legislation.

There are additional requirements for the Senate to pass this bill with a simple majority: It must have the effect of lowering the deficit, and it can’t drastically change existing legislative policies. The latest estimate from the nonpartisan Congressional Budget Office estimated that the AHCA would indeed trim the deficit by about $150 billion over a ten-year period, but that was before the bill was amended to include nearly $150 billion in federal support to state-level “high-risk pools” for individuals with pre-existing conditions or other factors that make insurance difficult to afford.

That opt-out amendment also lets states choose to exempt their insurers from requirements for covering a number of “essential” health benefits, including prescription drugs and hospitalization. Some argue that this opt-out plan crosses the line into setting policy, which would require the more traditional 60 vote majority in the Senate. To adjust either of these concerns, the Senate would likely need to revise the bill as it was passed by the House.

The fact that no one has any firm idea on which states might opt out, and to what extent, casts doubt on whether or not the CBO will be able to provide an accurate estimate on the costs and affect on insurance enrollment.

Even if the bill passes parliamentary muster, there are several Republican members of the Senate who have voiced skepticism or caution about rushing into a vote.

Sen. Lindsey Graham (SC) Tweeted earlier today that while he appreciates the House’s efforts on healthcare reform, he’s “concerned with the process.”

“A bill — finalized yesterday, has not been scored, amendments not allowed, and 3 hours final debate — should be viewed with caution,” Graham wrote in a follow-up Tweet, before going on to argue that the most effective way to bring about a true bipartisan effort would be to let the Affordable Care Act truly fail.

Graham is one of a handful of senators who supported an alternative repeal and replacement plan, the Patient Freedom Act, introduced in January by Sen. Bill Cassidy (MD).

Sen. Susan Collins of Maine, a co-sponsor of that bill, has publicly expressed concern about how the AHCA may leave large numbers of rural Americans without insurance. Collins, along with Alaska’s Lisa Murkowski, were the only two Republicans to vote with Democrats against a bill to cut funding to Planned Parenthood. The AHCA, in its current form, would effectively block all federal funding to Planned Parenthood.

Before the AHCA was unveiled, Tennessee Senator Lamar Alexander was among those calling for a bipartisan approach to reforming healthcare, likening it to a collapsing bridge.

“You send in a rescue team and you go to work to repair it so that nobody else is hurt by it and you start to build a new bridge, and only when that new bridge is complete, people can drive safely across it, do you close the old bridge,” said Alexander in February. “When it’s complete, we can close the old bridge, but in the meantime, we repair it.”

Today, Alexander congratulated his House colleagues while cautioning that the Senate “will take the time to get it right.”

In his statement, Alexander laid out four goals for the Senate bill: making sure people will have options; lowering insurance premium costs; gradually giving states more flexibility on Medicaid while not pulling the “rug out from under people who rely on Medicaid”; and making sure people with pre-existing conditions have access to insurance.

On the opposite end of the spectrum are more hard-line conservative Senators, like Rand Paul (KY), Texas’s Ted Cruz and Mike Lee (UT), who openly criticized the original iterations of the AHCA as “Obamacare Lite,” as opposed to the full repeal of the bill they hoped to see. Today, Cruz called the House vote “an important step,” and said the Senate “should continue to improve the bill.”

Earlier this week, Sen. Majority Leader Mitch McConnell acknowledged that passing this bill in the Senate “will be a real big challenge.” Today he reiterated his support of the idea of repealing and replacing Obamacare, but without specifically saying anything positive about the AHCA.

McConnell’s statement does note that the Senate will take up the bill after “the completion of procedural and budgetary scorekeeping reviews.”

Assuming the Senate is able to hammer out compromises that produce a bill that’s acceptable to all factions in the Senate, the AHCA would go back to the House, as both chambers of Congress need to agree on the resolution before it can be passed on to the White House.

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.