What happens when millions of voters find out that they’re being denied a federal benefit because of where they live?

What happens when voters in Alabama discover that they won’t get the same subsidized insurance as their cousins in Kentucky because elected Republicans have decided it wasn’t a good idea? What happens when voters in Georgia recognize that they’re still paying for Medicaid expansion but will get none of the savings that could come from covering the uninsured? What happens when South Carolinians hear their Tea Party has singlehandedly stopped tens of millions of health care dollars from being flushed into their economy?

President Obama is about to begin his next “big campaign“: getting seven million uninsured people to sign up for health care when the Affordable Care Act open enrollment begins on October 1.

Around this time, millions of Americans who currently make too much to qualify for Medicaid but earn under 133 percent of the poverty level will begin to find out that the subsidized insurance they’re entitled to under the Affordable Care Act has been rejected for them by their states’ Republicans.

Despite polls showing Obamacare still about as popular as it was when it was passed, this unprecedented moment is fueling optimism in Democratic activists who see “a once-in-a-generation opportunity” in the at least 24 states where Medicaid will not be expanded. Hopes are up because of new polling that shows expansion is very popular, even in the reddest states in the Union:

Daily Kos‘ mdmslle wrote, “This is an opportunity for Democrats to get ahead on this issue in states where people will see changes in coverage and where the GOP will continue to try to blame Obama and the Democratic health reform initiative. We can fight back.” She is trying to lead a movement in these states to let voters know that the only thing standing between them and a more humane health care system is their states’ Republicans.

This new wave of optimism about the Affordable Care Act is buoyed by good news from California about rates and the feeling that Republicans’ constant predictions of disaster have lowered voters’ expectations to the point that anything short of “Armageddon” will be a relief.

The New York Times‘ Paul Krugman summarized that positive outlook from the left on Obamacare like this:

Still, here’s what it seems is about to happen: millions of Americans will suddenly gain health coverage, and millions more will feel much more secure knowing that such coverage is available if they lose their jobs or suffer other misfortunes. Only a relative handful of people will be hurt at all. And as contrasts emerge between the experience of states like California that are making the most of the new policy and that of states like Texas whose politicians are doing their best to undermine it, the sheer meanspiritedness of the Obamacare opponents will become ever more obvious.

Republicans wouldn’t dare to reject a new Medicare benefit on a state-by-state level for one simple reason: Seniors vote.

If it turns out that Medicaid expansion drives the working poor and those who empathize with them to the polls in droves, the right’s worst nightmares about Obamacare may come true in 2014.