Obamacare might be on its last legs. A new president and a new Congress promise to repeal and replace the healthcare legislation. The potential demise of the Affordable Care Act has caused some stocks of companies that have become dependent on its benefits to suffer. Here's why Community Health Systems (CYH 4.02%)Tenet Healthcare (THC 1.99%), and Centene (CNC 1.15%) stand out as three of the worst Obamacare stocks in 2016. 

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Hospital headwinds

Community Health Systems' stock essentially collapsed this year, plummeting by 75%. Roughly one-third of that drop came after the November U.S. election results appeared to sound the death knell for Obamacare. The hospital chain has struggled throughout 2016, however.

The 2014 acquisition of HMA hasn't gone as well as expected. While many predicted that Obamacare would result in lower write-offs due to patients not paying their hospital bills, Community Health Systems has increased its allowance for doubtful accounts. The company has also had to deal with its heavy debt load.

This last issue resulted in Community Health spinning off 38 of its hospitals in less populated areas and its consulting business into a separate entity, Quorum Health Corporation (QHC). The transaction, which was finalized in April, generated around $1.2 billion, much of which Community Health used to pay down debt.The company continued to make other divestitures in subsequent months.

After continuing to disappoint investors throughout the year, Community Health announced in September that it was "exploring a variety of options with financial sponsors, as well as other potential alternatives." These discussions were in a preliminary stage at the time. Since the announcement, no further details have been made public by the company.

Lawsuits, losses, and loads of debt

Another hospital operator, Tenet Healthcare, saw its shares plunge nearly 50% in 2016. The U.S. elections took a big toll, with around half of the stock's decline coming after the surprising outcome that could wind up sealing Obamacare's fate.

Tenet also faced other significant challenges. The company reported second-quarter results that were much worse than what Wall Street expected. It then followed up in the third quarter with yet another big disappointment.

One major issue that impacted Tenet's bottom line stemmed from criminal and civil litigation related to referral source arrangements at three of the company's former hospitals and one current hospital. In August, Tenet announced a settlement agreement in which it agreed to pay $517 million.

Like Community Health Systems, Tenet has amassed a sizable amount of debt. In November, the company added to its debt with a $750 million private offering of senior secured second lien notes. 

Medicaid Mayday

Unlike Community Health and Tenet, Centene's stock was actually up a little year to date at the beginning of November. However, the election results caused the managed care provider's shares to sink. Centene's stock is now down around 15% this year.

The primary concern for Centene is that a repeal of Obamacare could roll back the expansion of Medicaid in many states. Nearly 60% of Centene's total membership comes from Medicaid programs.

However, the managed care provider also has a significant presence in the Obamacare individual insurance exchanges. Centene's acquisition of HealthNet in March increased its commercial membership more than tenfold.

The company's expertise with the Medicaid population enabled it to create plans that were more appealing to lower-income customers participating in the Obamacare exchanges. As a result, Centene became one of the more successful insurers under Obamacare.

With Obamacare in jeopardy, Centene faces a double whammy. It stands to lose some of its Medicaid membership as well as potentially lose individual insurance members depending on what happens in Washington, D.C.

Biggest loser in 2017?

Which of these three worst Obamacare stocks of 2016 could be the biggest loser next year? My pick is Centene. 

If all federal dollars for the Obamacare Medicaid expansion are eliminated, it could be a nightmare scenario for Centene. Even though the states that have expanded Medicaid under Obamacare pick up part of the costs, the federal government still subsidizes 97% of the expansion costs in 2017, decreasing gradually to 90% in 2020 and afterward. Bad news for Obamacare means bad news for Centene.