Democratic candidates want to expand government-provided health care, and this is bad medicine. With the Democratic presidential debates resuming this week, health care reform is in the spotlight, and Sen. Kamala Harris is trying to set herself apart from others by adding a private Medicare Advantage option to her “Medicare for All” plan, drawing the ire of Sen. Bernie Sanders.

By doing so, she is attaching her plan to a winner. Medicare Advantage is growing, doubling since 2010 to more than 20 million patients, which is more than a third of all Medicare enrollees. This, despite the fact that Obamacare cut federal grants to Medicare Advantage by billions of dollars in order to help pay for expanding Medicaid coverage and subsidies for the state exchanges. Nevertheless, Medicare Advantage has continued to expand, generating billions of dollars of profits for insurance companies while at the same time expanding choice for the consumer (to about 3,700 plans from 3,100 the prior year).

This is a public/private partnership at its best, so it is not surprising that Ms. Harris wants to incorporate it as an option into her Medicare for All plan, thereby setting her plan aside from Mr. Sanders’ or Elizabeth Warren’s strict Medicare for All plan. But even with this improvement Ms. Harris’ still destroys the employer-based health system which currently provides insurance for more than 170 million people. This insurance still involves bureaucratic hurdles but is nevertheless much easier for a primary care doctor like me to work with. It also pays me and my hospital more, and regulates us less. It provides better access to health care tests and treatments than either Medicare or Medicaid does.

Trumpcare stands in contrast as a refreshing market-based alternative to the government expansion central to all of the Democrats’ health care plans, including even former Vice President Joe Biden’s, who would expand Obamacare and create a public option while providing coverage for undocumented immigrants. Keep in mind that bigger government means more regulations, less access, longer waiting lines, lower reimbursements and fewer satisfied patients or providers.

By contrast, the president and his administration have focused on more price transparency, more generic drugs (close to 1,000 approved last year by the FDA, the most on record), and the defunding of the Obamacare individual mandate. This was the most important move of all, since it mandated that patients buy a policy with high deductibles and high premiums that provided 10 essential benefits they might never need. More than 6 million people a year took the tax penalty rather than sign up for Obamacare, a sure sign it wasn’t working.

Now, in the post-mandate era, the Trump administration is starting to introduce short-term skinny plans, longer-term association plans that work across state lines, and waivers for states that would like to try a different kind of approach, including direct-care models. The result will be more choice among patients, more competition among insurance companies and, ultimately, lower cost and higher quality.

Also coming up is a focus on prevention and better quality outcomes for kidney disease (more home dialysis, more transplants), HIV (prevention and early diagnosis), and of course the opioid epidemic, which is leading to a marked decrease in prescriptions written and overdose deaths dropping (5 percent) for the first time since 1990.

Opponents may call this a fragmented approach to health care, but I call it working with the existing system and strengthening it by adding more low-cost options. Obamacare, a small part of the health insurance system, is still surviving and its premiums are flat for the first time.

I spoke with Health and Human Services Secretary Alex Azar last week who expressed the president’s overriding theme, “the president has a holistic vision on health care. He intends to protect what works and fix what’s broken. To protect private insurance and Medicare — covering 240 million people — from anyone who is trying to attack it. Pre-existing conditions will be covered. We will continue to work on improving quality with price transparency, deregulation, new billing practices, and more.”

By contrast, the Democratic candidates for president want to expand government provided-health care to either plug the gaps or replace the whole system. This would be both bad politics and bad medicine.

• Marc Siegel, a physician, is a clinical professor of medicine and medical director of Doctor Radio at NYU Langone Medical Center. He is a Fox News medical correspondent.