(CNN) Despite President Donald Trump's celebration in the White House Rose Garden last week, Republicans still have a long way to go before they can finally make good on their promise to dismantle Obamacare.

Passing a health care bill out of the House was the first step, but now the challenge of guiding a bill through the Senate -- where Republicans have an even slimmer majority -- begins. Republican senators have already said they will craft their own legislation and will use a process known as budget reconciliation to move it out of the upper chamber with 51 votes instead of 60, but that approach gives Majority Leader Mitch McConnell little room for error. Republicans can only afford two defections in their ranks.

Here are the five flash points you can expect as the Senate Republicans debate their way forward on health care:

Medicaid

Medicaid has long been in conservatives' crosshairs, but the benefit for states has been undeniable. Medicaid expansion has been a lifeline for constituents who suffer from mental illness or addiction and have been able to access treatment through the expansion.

Of the 52 Republicans in the Senate, 20 hail from states that expanded Medicaid in recent years.

Ohio's Rob Portman, Alaska's Lisa Murkowski, West Virginia's Shelley Moore Capito and Colorado's Cory Gardner sent a letter to McConnell in March, when the House's bill was first released, expressing their concerns with the way the House bill handled Medicaid expansion.

The House's plan would end enhanced federal funding for Medicaid expansion in 2020. After that year, individuals on the program weren't kicked off, but once they cycled off the program, they weren't allowed to re-enroll. Essentially, the House's bill phased out Medicaid expansion over time.

The bill would also curtail federal support for the overall Medicaid program, giving states either a set amount of money per enrollee or a fixed block grant -- shifting the financial burden to the states.

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Expect in the Senate that many of the lawmakers whose constituents have benefited from the Medicaid expansion will fight to keep the program intact longer. They will want to give individuals more time to transition off Medicaid and provide additional safety nets to ensure that people who may become ineligible for the program have another means to buy insurance. Meanwhile, expect Republicans who came from states that didn't expand Medicaid to argue that the program be phased out as soon as possible to save money.

Tax credits

One of the earliest controversies in the House's health care bill was the issue of tax credits. Conservatives argued the House's refundable tax credits were little more than a new entitlement program, a new name for the Obamacare subsidies Republicans had railed against for years. The similarities between the two -- Obamacare subsidies are also refundable tax credits -- prompted some lawmakers to dub the House plan "Obamacare Lite."

But more moderate Republicans argued that refundable tax credits in the House bill were inadequate -- largely because the tax credits were based on age, not income.

As CNN reported at the time when the Congressional Budget Office released its initial score of the House's bill, a 64-year-old making $26,500 would pay $1,700 for coverage in 2026 with Obamacare subsidies. But under House Speaker Paul Ryan's plan, that same person would pay $14,600 in premiums with the GOP tax credits.

In an attempt to lower the burden for low-income and older Americans, expect some GOP senators to push for some sort of means testing, which would take into consideration someone's income when calculating the size of their tax credit. In March, South Dakota Republican Sen. John Thune, a member of leadership and a member of the health care working group, introduced a proposal along those lines targeted to boost the size of tax credits for lower income people.

Planned Parenthood

The House health care bill would defund Planned Parenthood for one year, a provision that could face increased scrutiny in the Senate where some moderate lawmakers like Sens. Lisa Murkowski of Alaska and Susan Collins of Maine have already said they'd prefer to keep funding the women's health care provider.

"I, for one, do not believe that Planned Parenthood has any place in our deliberations on the Affordable Care Act," Murkowski told state lawmakers in Alaska in a speech earlier this year. "Taxpayer dollars should never be used to pay for abortions, but I will not vote to deny Alaskans access to the health services that Planned Parenthood provides."

Taking the provision out could alienate the Senate's conservatives who viewed the House's funding repeal as a major victory and are now feeling pressure from outside religious groups to keep the defund in the Senate's version of the bill.

Pre-existing conditions

One key Obamacare-era regulation that would be changed dramatically under the House's health care bill protects people with pre-existing conditions.

The promise of protecting people with pre-existing conditions was at the epicenter of Trump's own campaign stump speeches. But under the House's health care bill, states would be able to opt out of the community rating protection, which would allow insurers to base premiums based on a person's medical history. This would only apply to those who are not continuously insured.

Experts have argued that it could have major ramifications for people with pre-existing conditions.

Expect moderate Republicans to take a serious look at how to make sure that people with pre-existing conditions have additional safeguards as they craft their own bill. The messaging for Republicans has already been brutal as Democrats have very publicly argued that Republicans are gutting an overwhelmingly popular protection from the Affordable Care Act.

Essential Health Benefits

Under Obamacare, insurers are required to cover 10 key benefits for consumers. Those range from hospitalization to maternity care, but the House health care bill changes that. In an attempt to drive down premiums, the House's conservative Freedom Caucus insisted that states be able to opt out of the essential health benefits requirements.

Conservatives in the Senate are expected to push for even more robust insurance deregulation in an attempt to lower premiums. One idea being considered would give states an "opt in" rather than an "opt out" on key Obamacare-era regulations like requiring insurers cover the 10 essential health benefits.

But that could stir concerns from moderate senators who already fear that the GOP has gone too far to scale down insurance protections for consumers back home. Waiving the essential health benefits could hurt people with pre-existing conditions because insurers could opt not to cover their treatment. Also, it could make it harder for those dealing with substance abuse or mental health issues to get help.