After it was announced last week that more than eight million people have used ObamaCare's online marketplaces to enroll in health insurance, Democrats face a big choice ahead of the midterm elections: Do they stop talking about ObamaCare with the hope that Republicans stop bashing the law? Or do they finally embrace the law and tout its benefits?

President Obama made his preferences clear at a press conference last week: "I don't think we should apologize for it, and I don't think we should be defensive about it. I think there is a strong, good, right story to tell."

At the same time, Republicans say they're not done bashing the law. They think it's an issue that will help them regain control of the Senate.

But unlike for most of the last three years, the facts are now firmly on the side of Democrats.

While more than eight million people have already signed up for health insurance through the ObamaCare exchanges, experts predict that number will rise to over 20 million by the next presidential election.

In addition, millions more have gained health insurance through expanded Medicaid programs or by being able to stay on their parents' health insurance plans.

That's a lot of people who are counting on ObamaCare.

Meanwhile, Republicans have no alternative. They insist they still want to repeal the law but after half a decade of debate, they still have no idea what they'll put in its place.

And some GOP lawmakers are starting to worry.

Here's Rep. Dennis Ross (R-Fla.) at a town hall meeting: "I wish we had an alternative. You know what's unfortunate? It's for the next six months, we're going to go into an election knowing that we're not going to do anything to address health care because we've gone so far for the last three years saying 'no,' that we don't have an alternative to say 'yes' to."

He added: "I think that the American public, when they go to vote, they're going to look at credibility before they look at substance."

Democrats are winning on credibility. But the big question is will they stand up and fight for substance in this year's elections?