By Tom Coburn

Obamacare supporters are touting reports that 6 million Americans bought insurance on exchanges as evidence the plan is moving in the right direction. But these numbers are misleading. If anything, they show that Obamacare's greatest challenges are yet to come.

Of these enrollees, as many as 89% were previously insured. Helping 5 million Americans re-enroll in insurance is no great achievement, particularly when many of those customers were forced to give up plans they liked.

For everyone else, costs continue to skyrocket. President Obama promised to lower health premiums by $2,500 per family, but premiums have increased by more than that since Obamacare passed. The costs of deductibles and premiums — big, out-of-pocket expenses — have soared more than 40% in only one year. Premiums will likely increase even more because young, healthy people aren't enrolling fast enough to offset the costs of covering older, sicker patients.

Obamacare is proving, yet again, the axiom that the best way to make something expensive is for government to make it affordable.

Meanwhile, for millions of patients, Obamacare itself has become a pre-existing condition. Patients have been left with fewer choices and limited access to the best hospitals and care.

Sadly, Obamacare is about cutting choices rather than costs. That's why only 26% of Americans now support the law.

Ironically, no one has done more to repeal Obamacare than President Obama. He has changed key provisions of the law more than a dozen times. While supporters claim these changes are about protecting patients, it's no accident they are being timed in a way to protect vulnerable Democrats who are up for re-election.

It's time for policymakers to start over. The plan I recently introduced with Sens. Richard Burr, R-N.C., and Orrin Hatch, R-Utah, the Patient CARE Act, will exceed all of Obamacare's goals by giving individual Americans the freedom to shop for their own health care. Markets aren't perfect but, as Obamacare has shown, they are far more effective than government coercion.

Sen. Tom Coburn, R-Okla., is a medical doctor and one of three authors of a GOP alternative to Obamacare.