NEW YORK (Reuters) - Republican President-elect Donald Trump vowed on the campaign trail to repeal Obamacare, but making good on that promise may be easier said than done. President Barack Obama’s 2010 national healthcare reform law extended medical insurance to 25 million more people by expanding the Medicaid plan for the poor and creating subsidized coverage for individuals. Republican lawmakers, who have voted more than 50 times to repeal all or part of the law, have begun pressing Trump to deliver. Senate Majority Leader Mitch McConnell said on Wednesday repealing Obamacare is a “pretty high item on our agenda” for the new Congress. But a complete repeal of Obama’s Affordable Care Act may not be immediately in the cards, as Republican lawmakers now hold 51 seats in the Senate at latest count, well short of the 60 seats required to overturn it. Instead, health policy experts said, Trump could try to dismantle key elements through a process called budget reconciliation. That would allow him to eliminate funding for the income-based subsidies that make the new insurance plans affordable, or cut the money providing expanded Medicaid benefits in 31 states. “Some of the policy experts on the Republican side would say tearing it up and starting over would be very disruptive,” said Paul Howard, director of health policy at the conservative Manhattan Institute. Parts of the law have been weakened through legal challenges. Several of the largest U.S. health insurers have pulled out of the exchanges for individual coverage after losing money on a sicker-than-expected group of patients. Consumers not eligible for government subsidies have seen premiums rise sharply, including a projected average increase of 25 percent for 2017. Scrapping the law altogether without a clear plan for providing replacement coverage for so many people would be politically risky, experts said.  Trump also would face a tight deadline were he to try to dismantle the insurance exchanges by 2018; many state-based health insurance regulators require insurers to submit plans for the upcoming year by April or May - only a few months into a new administration. Trump also could seek changes to other provisions of the law, such as a tax on medical device makers, or the so-called “Cadillac tax” that is due to hit rich employer-based healthcare plans in 2020. However, some elements could not be eliminated by depriving the law of funds. For instance, the law prevents insurers from denying coverage to people based on their health or pricing insurance based on gender. Mandatory coverage of preventive benefits also would be unaffected - short of a complete repeal. It also is not clear if Trump would try to reverse the individual mandate, which requires people to purchase health insurance or pay a penalty. The goal of the requirement was to broaden the pool of policyholders to include more healthy Americans. Aetna Chief Executive Officer Mark Bertolini said on Thursday at a New York Times Dealbook conference that some elements of the law are so popular that they are likely to continue, even if there is something Trump calls “repeal.” They include allowing young adults to stay on their parents’ plans and people with health problems to buy insurance without paying more. Medicaid could continue to expand, he said, though with a different type of federal financing. Trump’s surprise victory over Democratic candidate Hillary Clinton rattled healthcare investors on Wednesday, depressing shares in hospital operators and some insurers. Medicaid focused health insurer Molina Healthcare Inc. fell nearly 16 percent, and hospital chain Tenet Healthcare Corp dropped 25 percent. Large insurers, who have been losing money on the exchanges, gained, with Anthem Inc. up 1.5 percent. Enrollment opened on Nov. 1 for 2017 coverage and once those plans are purchased, it would be legally difficult for Trump to cancel them before the one-year contracts run out, said Molina Healthcare Chief Executive Officer Dr. Mario Molina. “Any changes they make will have to be on a prospective basis to begin in 2018,” Molina said. It’s not clear what Trump’s plan to replace Obamacare would look like. Options he raised on the campaign trail include replacing the Obamacare individual coverage with high-deductible healthcare plans, and lumping the sickest people together into high-risk pools that are insured separately. “I think there is going to be a lot of confusion and a lot of anxious people,” Molina said. Among the worries for some people covered under Obamacare is how long it will last. Before the law took effect, Marc Dobin, a 57-year old mediator and lawyer in Jupiter, Florida, said his insurer put a surcharge on his premium because he has heart stents. Under Obamacare, insurers are barred from charging more for pre-existing conditions. “Imagine the disaster if, part way through the year, they cancel it,” Dobin said. For others, the cost of premiums bolstered their support for Trump. Crista Simmons, 63, a piano teacher in Kalamazoo, Michigan, spends about a third of her gross income on premiums and medical care. “There are people who pay more in premiums than their mortgage,” she said. 