The Democrats who wrote and passed the Affordable Care Act were sure of two things: The law had to include a mandate requiring every American to purchase health insurance, and it had to have an enforcement mechanism to make the mandate work. Enforcement has always been at the heart of Obamacare.

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Now, though, enforcement time has come, and some Democrats are shying away from the coercive measures they themselves wrote into law.

The Internal Revenue Service is the enforcement arm of Obamacare, and with tax forms due April 15, Americans who did not purchase coverage and who have not received one of the many exemptions already offered by the administration are discovering they will have to pay a substantial fine. For a household with, say, no kids and two earners making $35,000 a piece, the fine will be $500, paid at tax time.

That's already a fact. What is particularly worrisome to Democrats now is that, as those taxpayers discover the penalty they owe, they will already be racking up a new, higher penalty for 2015. This year, the fine for not obeying Obamacare's edict is $325 per adult, or two percent of income above the filing threshold, whichever is higher. So that couple making $35,000 a year each will have to pay $1,000.

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There's another problem. The administration's enrollment period just ended on February 15. So if people haven't signed up for Obamacare already, they'll be stuck paying the higher penalty for 2015.

By the way, Democrats don't like to call the Obamacare penalty a penalty; its official name is the Shared Responsibility Payment. But the fact is, the lawmakers' intent in levying the fines was to make it so painful for the average American to ignore Obamacare that he or she will ultimately knuckle under and do as instructed.

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Except that it's easier to inflict theoretical pain than actual pain. Tax filing season is enlightening many Americans for the first time about the "mechanics involved" in Obamacare's fee structure, Democratic Rep. Lloyd Doggett wrote to the Centers for Medicare and Medicaid Services on December 29. "Many taxpayers will see the financial consequences of their decision not to enroll in health insurance for the first time when they make the Shared Responsibility Payment."

That is why Doggett, who has since been joined by fellow Democratic Reps. Sander Levin and Jim McDermott, asked the administration to create a new signup period for anyone who claims ignorance of the penalty. On Friday, the administration complied, creating a "special enrollment period" from March 15 to April 30.

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To be eligible, according to an administration press release, people will have to "attest that they first became aware of, or understood the implications of, the Shared Responsibility Payment after the end of open enrollment … in connection with preparing their 2014 taxes."

It's not the most stringent standard: Just say you didn't know. But even with that low bar, a significant number of Americans will decide not to enroll in Obamacare. For some, it's the result of a financial calculation; paying the fine is cheaper than complying. Others are unaware. Maybe a few are just defiant.

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Whatever the reasons, quite a few people will be hit with the penalty; Doggett and his Democratic colleagues subscribe to the Treasury Department's estimate that somewhere between three million and six million Americans will have to pay the Obamacare penalty on the tax forms they're filing now. Many will owe more next year, when the penalty goes even higher in 2016.

The individual mandate has always been extremely unpopular. In December 2014, just a couple of months ago, the Kaiser Family Foundation found that 64 percent of those surveyed don't like the mandate. The level of disapproval has been pretty consistent since the law was passed.

And there's very little chance the individual mandate's approval numbers will improve, now that millions of Americans are getting a taste of what it really means. They're learning an essential truth of Obamacare, which is that if you don't sign up, the IRS will make you pay. No matter how much some Democrats would like to soften the blow they have delivered to the American people, that's the truth about Obamacare.