This was published as a Wall Street Journal Think Tank column on October 9, 2014.

If the Congressional Budget Office is close to the mark, in the second open-enrollment season we will see about a doubling of the 7 million people enrolled in the Affordable Care Act insurance marketplaces. Open enrollment, which begins Nov. 15, is three months this year, or half as long as last year, and the remaining eligible uninsured are a more difficult-to-reach population. Here are the biggest challenges this time around:

First, the overwhelming reason the remaining uninsured cite as to why they have not already gotten coverage is that they believe they could not afford it. The message that most needs to reach the uninsured is that there are tax credits available to help make coverage more affordable. For a 30-year-old making $25,000 per year, the ACA tax credit would reduce the average cost of the most commonly selected “silver plan” from $2,877 per year to $1,729. Eighty-five percent of those who got coverage in the new insurance exchanges qualified for credits this year, but in our Kaiser Family Foundation survey of the uninsured in California, 73% of those eligible for assistance did not know they could get help.

Second, the uninsured need to know that the penalty for going without coverage increases substantially next year, to $325 per person or 2% of income (whichever is greater). Our survey shows that 66% of the uninsured are aware of the penalty.

Third, the first-year’s experience showed that personal assistance was essential to getting many uninsured people enrolled. That will be even more true for the remaining uninsured, who are more likely to have been uninsured for a long time or have never had insurance, who have language barriers, or who worry about family members’ immigration status. Somewhat less federal money is available this year to support community-based outreach and enrollment assistance.

Fourth, the news media are the primary source of information about the ACA for the public and the uninsured. Media coverage, even negative reporting, gets people talking about the health-care law. As the ACA cools as a political issue, the falloff in coverage–including negative stories–may cause fewer uninsured people to want to check out their coverage options.  Other forms of marketing and outreach would need to compensate.

Fifth, people who enrolled in coverage the first year will be auto-enrolled in their same plans in year two unless they pick a new plan. But the plan they chose last year may no longer be the best deal for them. How many of the 7 million who enrolled in year one will shop again in year two?

Still other enrollment issues are on the horizon. The CBO estimates that expanded Medicaid enrollment under the Affordable Care Act will reach 11 million in 2015. But several Republican states, including Utah and Indiana, are negotiating waivers with the Obama administration to expand their Medicaid programs. And Pennsylvania, which has received a waiver, is likely to elect a Democratic governor more interested in a traditional Medicaid expansion. As long as state Medicaid programs can expand on terms that are acceptable to them, the appeal of 100% federal funding (eventually falling to 90%), and the need to cover their uninsured residents, may gradually trump ideology and dislike of Obamacare and the president in the 23 states that have not expanded Medicaid. If, say, after 2016 most or even all 23 states expand Medicaid, millions more low-income people would gain coverage.