Now that the government shutdown has ended and the president has preserved ObamaCare for the time being, it's worth explaining why my organization, the Heritage Foundation, and other conservatives chose this moment to fight—and why we will continue to fight. The reason is simple: to protect the American people from the harmful effects of this law.

I spent a good part of my summer traveling around the country with the Heritage Foundation's sister organization, Heritage Action, and I heard firsthand from many Americans being harmed by ObamaCare. More and more people have had their work hours cut, their jobs eliminated and their coverage taken away as a result of this new law.

Supporters of ObamaCare usually defend the law by insisting that they want to help people. I won't question their motives. I do wonder, however, if they understand what they're doing to the country.

We know that premiums are going up due to ObamaCare—Americans are getting notices in their mailboxes every day. On Wednesday, Drew Gonshorowski of the Center for Data Analysis at the Heritage Foundation published research that shows exchange premiums are going up in all but five states. In North Carolina, for example, many consumers will find their premiums almost double when shopping on the government exchanges. The hardest-hit states, such as Georgia, Arizona, Vermont and North Dakota, will see premium increases of up to 150%.

Mr. Gonshorowski's research shows that the hardest hit by the increases will be young adults. "A state that exhibits this clearly is Vermont," he writes, "where the increase for 27-year-olds is 144 percent and the increase for 50-year-olds is still 60 percent, but far less. All states exhibit this relationship."

We also know that, once established, the cost of ObamaCare's new entitlements will not fall. Historical evidence suggests the opposite. Nearly 50 years ago, at the time of Medicare's enactment, it was projected that the federal government would spend $9 billion on Part A hospital services in 1990. Actual spending in that year totaled $67 billion—an increase of 644% compared with initial estimates.

Likewise, government officials originally projected that Medicare Part B physician services would require "federal appropriations of about $500 million a year from general tax revenues." Last year, the federal outlay for that program was $163.8 billion—overshooting the original estimate by more than 4,400%.

Given this track record, the Congressional Budget Office's projection that ObamaCare will cost "only" $250 billion (you read that right: a quarter-trillion dollars) a decade from now seems far-fetched.

There's a reason Senate Majority Leader Harry Reid recently claimed that ObamaCare will lead to a single-payer health-care system: It happens to be true. Once employers drop health coverage for their low and middle-wage workers, the majority of Americans will be dumped into tightly regulated health exchanges and granted a "choice" of plans that will be more alike than different. The quality of care will suffer, access to doctors and plans you once had and liked will be reduced, and America will deteriorate into a two-tier health system—one in which the well-off can still buy quality coverage, but most Americans are consigned to poor care through the exchanges and Medicaid.

Yes, I can hear many conservative friends saying to me right around this point: "Jim, we agree with you that ObamaCare is going to wreck the country, but elections have consequences." I have three responses.

The first is that ObamaCare was not the central fight in 2012, much to the disappointment of conservatives. Republicans hoped that negative economic news would sweep them to victory, and exit polls confirmed that the economy, not health care, was the top issue. The best thing is to declare last year's election a mistrial on ObamaCare.

Second, the lives of most Americans are not dominated by the electoral cycle. They shouldn't have to wait three more years for Congress to give them relief from this law, especially when the president has so frequently given waivers to his friends. Full legislative repeal may not be possible while President Obama remains in office, but delaying implementation by withholding funds from a law that is proven to be unfair, unworkable and unaffordable is a reasonable and necessary fight.

There's a third reason not to stop fighting. Forget the consultants, the pundits and the pollsters; good policy is good politics. If the Republicans had not fought on ObamaCare, the compromise would have been over the budget sequester. Instead, they have retained the sequester and for the past three months ObamaCare and its failings have been front and center in the national debate. Its disastrous launch was spotlighted by our defund struggle, not overshadowed, as some contend. With a revived and engaged electorate, ObamaCare will now be the issue for the next few years.

These are the reasons we fought so hard to get Washington to listen to the American people and take action to stop ObamaCare, and it is why so many are thankful for the courageous leadership of people like Sens. Ted Cruz and Mike Lee, and conservatives in the House of Representatives. The law is economically unstable, financially irresponsible and harmful to hardworking Americans.

- Mr. DeMint, a former senator from South Carolina, is president of the Heritage Foundation.