The U.S. House is racing to find enough votes for its health-care bill this week, but even if it passes, prospects in the Senate have only darkened.

More than enough Senate Republicans oppose the House bill to kill it – with rival camps insisting on pulling the bill in opposite directions to meet their demands. With just a 52-48 majority, the bill would fail if three or more Republicans vote against it.

Republican leaders face a conundrum: If they move the bill to the right, moderates go running; move it to the left, and conservative opponents dig in.

Whether Republicans would actually tank something they’ve promised for the past seven years is unclear. All of them say they want something to pass, and House leaders unveiled tweaks to the bill Monday evening.

A look at how Senate GOP opposition to the measure breaks down:

Conservatives demanding fuller repeal

A trio of Senate conservatives has attacked the bill vociferously and said they will not vote for it without changes. At least one of the three – Rand Paul of Kentucky, Ted Cruz of Texas and Mike Lee of Utah – has to vote for the bill for it to pass, given united opposition from Democrats.

Paul, who has libertarian leanings, has slammed the bill as “Obamacare lite.” He criticizes it in part as too generous to people who don’t make enough money to pay income taxes, and has urged conservatives in both chambers to withhold their support for negotiating leverage, citing tactics from Donald Trump’s book “The Art of the Deal.” Trump, in turn, has called Paul on more than one occasion as part of what Paul calls a mutual-wooing operation.

Cruz complains the bill could actually lead to higher premiums next year because it doesn’t repeal Obamacare’s insurance mandates – the most costly of which is a ban on pre-existing conditions – and has tried so far without success to get Republicans to embrace a bolder repeal that would include Vice President Mike Pence overruling the Senate parliamentarian on what can be included in the package under the rules.

“I cannot vote for any bill that keeps premiums rising,” he said Sunday on CBS’s Face the Nation.

Defenders of Planned Parenthood

If McConnell and Trump manage to win over at least one of the members of the conservative trio, they still have numerous hurdles to clear among the party’s moderate camps.

Two Senate Republicans, Susan Collins of Maine and Lisa Murkowski of Alaska, oppose the House bill’s provision defunding Planned Parenthood – enough to bring the bill to the brink.

Defunding Planned Parenthood has been a major Republican priority for years, and losing that provision could cost conservative votes.

Protecting Medicaid expansion

A broader group has expressed concerns about the House’s plans to phase out Medicaid expansion money for their states, including Murkowski, Rob Portman of Ohio, Shelley Moore Capito of West Virginia and Cory Gardner of Colorado.

Dean Heller of Nevada – the Democrats’ No. 1 target in 2018’s midterm elections and the only Republican running in a state won by Hillary Clinton – declared Friday in a statement he couldn’t vote for the House bill as written because of Medicaid concerns expressed by four Republican governors, including Nevada’s Brian Sandoval.

The House bill would phase out that expansion starting in 2020 – part of an larger plan to cut Medicaid by $880 billion and taxes by $883 billion over a decade.

Some conservatives have demanded an earlier phaseout, something that could make it even harder for those senators to support the measure. It also makes potential swing voters out of senators from Arkansas, Nevada, Alaska, Colorado, Ohio and Louisiana – all states that expanded Medicaid.

Other holdouts

Bill Cassidy of Louisiana says he wants to radically reshape the House bill so that it covers more people, not the 24 million fewer estimated by the Congressional Budget Office.

“Society is going to pay for health care whether it is through insurance or not,” he said last week. “Society will pay for it either through cost-shifting to the privately ensured or it will pay for it through enhanced disproportionate payments” to hospitals that treat indigent patients.

Sen. Susan Collins and Sen. Bill Cassidy, R-La., introduced a health care bill in January that would allow states to keep the ACA or choose an option that would provide tax credits that are more generous than those in the plan proposed by House Republicans. Collins says she can’t back the House plan as it stands. Associated Press/J. Scott Applewhite

A doctor who worked for decades in a charity hospital, Cassidy crafted a bill with Collins that would keep most of the Affordable Care Act’s taxes and allow states to choose between keeping Obamacare largely as is or transition to a new system with more flexibility.

Cassidy has spoken emotionally and in depth about the importance of coverage, saying society pays one way or another when people go to the emergency room because they don’t have insurance, and criticizes the House bill for failing to meet President Trump’s campaign promise of insuring more people at a lower cost.

And then there’s Tom Cotton of Arkansas, normally a staunch conservative, who has emerged as a surprising wild card. He has warned House Republicans to go back to the drawing board because he thinks the bill could endanger the House majority and won’t pass the Senate.

Notably, Arkansas also has an enormous Medicaid expansion population and is one of the poorer states in the union.

State of play

The two toughest votes to get on each side may be Collins and Paul. Paul blitzed the bill even before it was released, when it was being drafted in secret and kept under lock and key, and he has shown repeatedly in the past he’s willing to be the only one in his party to oppose something on principle.

And it’s hard to square the House bill with the rhetoric Collins has used to describe it. She’s noted her state skews old, and the House bill hits older Americans now on Obamacare with premium hikes as high as 759 percent, according to the CBO, to pay for skimpier insurance. She told a local paper last week she couldn’t vote for the House bill as is.

If Paul and Collins both end up voting no, GOP leaders would have to win over everyone else. Leadership hopes could hinge on convincing Cruz and Cassidy to vote for the bill after getting a chance to amend the health bill, even if their amendments ultimately are defeated.

It’s also not clear how much of the House bill will be able to withstand the so-called Byrd rule, which prohibits provisions that aren’t principally budget related. That would potentially require parts of the bill to be rewritten on the Senate side anyway, and then sent back to the House. Final House passage also would be needed if broader amendments pass in the Senate.

Despite the obstacles, Senate Republican leaders say they’re still optimistic they can pass a bill – with Majority Leader Mitch McConnell noting last week that changes could be made during a “vote-a-rama” on amendments. He hopes to pass it before the April recess, bypassing Senate committees and going straight to the floor.

Bloomberg’s James Rowley contributed.