Now House Republicans really have managed to pass the American Health Care Act, the bill to replace Obamacare, this afternoon, the action shifts to the Senate — where you can expect the same dramas from the House’s months-long slog to pass their bill to play out again.

Except in the Senate, the margin for error is smaller. No Democrats will vote for a bill to weaken a signature Democratic achievement. And while Senate Republicans are using complex rules to pass a bill with a 51-vote majority, they can only afford to lose two votes.

House Republicans were able to torture the policy into something that won enough votes from the far-right and centrist wings of their conference to pass it in the lower chamber. But the same problems are going to crop up again in the Senate, where a critical mass of senators have already voiced concerns about the bill.

The bill still cuts Medicaid by $800 billion and rolls back Obamacare’s Medicaid expansion, which has covered millions of people in states represented by Republican senators. It is still expected to lead to upward of 20 million more Americans being uninsured. It still unwinds popular Obamacare protections for people with preexisting medical conditions.

The Senate has been content over the last few months to keep its head down and let the House take all the heat in its mad dash to construct a bill. But now the spotlight is on them.

“No,” Sen. Lindsey Graham (R-SC) told me plainly when I asked him this week if Senate Republicans were close to a cohesive plan that their conference would support.

The Senate’s big issue is going to be Medicaid

The final weeks of the House debate focused on protections for people with preexisting medical conditions who seek to buy private insurance. The amended bill allowed states to curtail some of those protections, with the tradeoff of additional funding that states could use to help insure people who are expensive to cover.

But in the Senate, you can expect Medicaid, the government program that insures upward of 70 million low-income people and was expanded by Obamacare, to take center stage.

The American Health Care Act, as currently constructed, phases out the expansion of Medicaid and changes the funding for the whole program by introducing a spending cap based on the number of people enrolled.

Combined, those changes are expected to cut Medicaid spending by more than $800 billion over the next 10 years and lead to 14 million fewer people being covered by the program.

Four Republican senators formally registered their problems with AHCA’s Medicaid provisions in early March, and others have raised their concerns. It’s not just Senate moderates — even reliably conservative senators from solid-red states that expanded Medicaid like Tom Cotton of Arkansas have signaled this is an issue for them.

Leaving a Capitol meeting with Vice President Mike Pence this week, Sen. Shelley Moore Capito of West Virginia, one of the GOP senators focused on Medicaid, said she didn’t think AHCA’s Medicaid cuts had been changed enough to satisfy her.

“My understanding is no, so I still have some issues that I think we need to work on,” she told me.

Senators are preparing changes, though details aren’t yet available. Sen. Rob Portman (R-OH) has been working on an amendment to tweak the Medicaid expansion phaseout, as first reported by Axios, but his office told me they did not yet have more details to share.

Sen. Bill Cassidy (R-LA), whose state has also expanded Medicaid under Obamacare, told reporters this week he was working on his own proposal to address Medicaid expansion but declined to go into detail.

Senators have problems with the AHCA’s private insurance changes too

The House GOP’s bill now allows states to waive Obamacare’s rule that prohibits insurers from charging people more for their insurance because of their health, with some strings attached. States are required to set up a high-risk pool where people with higher medical costs can buy health insurance, and people cannot be charged more if they don’t have a gap in coverage.

The protections for people with preexisting conditions is one of the most popular parts of Obamacare. Undermining them proved a mammoth problem in the House, overcome when leadership threw in an extra few billion dollars at the last minute to help people affected and win over moderates who had objected to the change. Experts doubt, however, that it’s actually enough to fully offset the increased costs that people could see.

That’s going to be an issue again for centrist Republicans in the Senate.

“It appears to be unclear how people with preexisting conditions would be treated under the bill,” Sen. Susan Collins of Maine, a critical swing vote who also objects to AHCA’s defunding of Planned Parenthood, told me. “That’s a major concern of mine.”

Graham also said that senators “still have differences on essential benefits” — the Obamacare requirement that plans cover certain health services, also allowed to be waived under the House bill — along with Medicaid expansion.

Senate Republican aides and lobbyists said the upper chamber is also likely to change the structure for subsidies, which help people afford private insurance, included in the House bill.

Obamacare offered help to people buying private insurance based on their income and location. AHCA switched that to subsidies based largely on age — younger people get less help, while older people get more — that are nonetheless less generous for lower-income Americans than those provided through the existing health care law.

The fear is that people who make less money or live in states with high medical costs could face soaring premiums because of the overhaul.

A 60-year-old making $20,000 a year living in Mobile, Alabama, currently receives a $13,000 subsidy under Obamacare. According to the Kaiser Family Foundation, that same person would receive a $4,000 subsidy through the Republican bill. But a 27-year-old making $75,000 a year, who currently receives no financial help through Obamacare, would now receive a $2,000 subsidy under the GOP plan.

Sen. John Thune (R-SD), a member of Senate leadership, has been working on an amendment to bolster the financial assistance for low-income Americans, as Axios reported last month. People making less than 250 percent of the federal poverty line (about $30,000 for an individual) would receive assistance based on both their age and income. People making more than that would receive only age-based subsidies, and the assistance would phase out the more money a person makes.

Conservative senators are going to want something out of this

Those changes to Medicaid and private insurance would steer AHCA back toward the middle and make it a less dramatic overhaul of Obamacare. So conservative senators are likely going to ask for something in return if they’re going to vote for it. Sens. Rand Paul of Kentucky and Mike Lee of Utah in particular have criticized the House bill at various stages of its development.

There have been reports recently that more state flexibility — building off the House bill’s provisions that now allow states to waive parts of Obamacare — could be introduced. Those changes eventually won over the conservative Freedom Caucus in the House.

But what exactly that would mean isn’t clear, and an aide to a conservative senator told me Thursday that they didn’t yet have details to share.

The bottom line is that the Senate is about to go through the same push-and-pull between its far-right and centrist wings that the House went through. The work is just getting started.

“I expect the Senate to do something different. I don’t expect we’ll vote on the House bill as it is,” Sen. Cassidy told Vox’s Sarah Kliff recently. “I expect we will put forward our alternative.”

And the drama doesn’t end there — whatever the Senate comes up with, the House will have to pass again. House Freedom Caucus leader Mark Meadows is already warning that it would be a problem for his colleagues if the Senate stripped out the House bill’s defunding of Planned Parenthood.

Meadows says he thinks it would be "problematic" for the Senate to send AHCA back to the House without defunding Planned Parenthood — Haley Byrd (@byrdinator) May 4, 2017

Some moderate House members have said they are relying on the Senate to fix problems they have with the House bill. But conservatives in the House could be driven away if the bill swings too far to the center.

The AHCA finallyed clear its first big hurdle on Thursday. But for Congress to actually follow through on repealing and replacing Obamacare, the work is far from done.