Twice, Barack Obama and his team put together winning national campaigns, combining sophisticated data analysis and effective marketing with a strong candidate. In a speech at the White House on Thursday morning, the president will launch a third such campaign, with a much weaker candidate: Obamacare. And this third campaign could be the one that defines Obama's legacy.

The details of Obama's speech will be familiar to those who've been paying attention to the evolution of the Affordable Care Act (the less popular actual name of the policy). The Huffington Post summarizes what to expect:

In his speech, Obama will highlight several of the law's consumer benefits, including the health insurance rebates given to 8.5 million people this year. He also will emphasize the effects of provisions the administration says enabled states including California, Oregon and Vermont to pressure health insurance companies to bring down their rates for next year, a senior administration official said.

Obama's problem is precisely that almost no one has actually been paying attention. Most of what people hear about Obamacare is unflattering: provisions are delayed, the House is voting to repeal it for the umpteenth time, or rhetoric from the president's opponents suggesting all sorts of horrible outcomes from its implementation. A June poll suggested that nearly half of Americans considered the law to be a bad idea. Twice as many people expected it would make them worse off than better off.

From the White House's perspective, the core problem is that getting people involved is critical to the legislation's success. There is a direct line between people being antipathetic to Obamacare and it failing to accomplish what was promised. Specifically: young people. If enough young, healthy people don't sign up for premiums in the marketplace established by the ACA, premiums will rise due to the expense of providing for older, less healthy participants. Which would undermine the core value proposition of the legislation. The Washington Post explains.

Young adults are the cheapest group to insure but the group most likely to go without insurance. The reason, put simply, is that young adults are likelier than any other group to be poor. Smith calculates that 19 million young adults between 18 and 34 lack health insurance. Under Obamacare, 8 million of them will qualify for free insurance through Medicaid. An additional 9 million will qualify for subsidized insurance in the exchanges. ...

Some young adults won’t find Obamacare a good deal, however. Because the program ends discrimination against the sick, limits it against the old and puts certain quality requirements on insurance, some healthy, young, not-that-poor people in the exchanges will find their premiums rising—a phenomenon known as “rate shock” in health-policy circles.

For the second year in a row, the president needs to get young people involved. Energized. He needs them to take action. But the sales job is trickier than in 2012—in part because Obama also needs these young people to spend money. The Post explained how Obama's old campaign apparatus is ginning back up for the task.

[Pollster David] Simas is focusing his formidable analytical resources on understanding this group. He begins clicking through a Powerpoint that holds reams of data on these young adults. “What do we know about them?” he says. “They’re overwhelmingly male.” Click. “They’re majority nonwhite.” Click. “One out of every three lives in California, Florida or Texas.” Click. “We have census maps breaking this down into the smallest geographic units.”

A couple more clicks and Simas is showing which television channels they like to watch (Spike TV, among others), which social-media platforms they use (Twitter, Facebook) and who they listen to (“No surprise. It’s mom.”). “We can figure out the message that works best for this group,” Simas says.

There's another stumbling block. Obama's campaign strength and the data on which it is built have both been used by his Republican as points of attack. Shortly after the actual campaign ended, the refrain of Obama's "eternal campaign" began, criticizing the president for using campaign-style tactics to persuade Congress to adopt his policy priorities. More recently, the campaign's data collection has been turned into a negative. In light of the recently exposed extent of the surveillance conducted by the National Security Agency, the campaign's use of data analysis like that Simas presented has been offered as a nefarious intrusion. During yesterday's House Judiciary Committee meeting, at least two Republican representatives mentioned the Obama campaign's use of data in a negative light.

If this new push isn't successful, if it doesn't inspire those young people to sign up for insurance, it's possible that the Obamacare roll-out itself could stumble. It's possible that a 2016 candidate could run against the failed policy, and work with a Republican majority in the Senate and House to repeal it. At stake, then, is Obama's signature legislation. His legacy. It doesn't all hinge on today's announcement, of course, but it might hinge on the upcoming marketing push. Obama's third national campaign could be most difficult, and most important.

Update, 1:00 p.m.: Surrounded by people who've benefitted from the Affordable Care Act's provisions, Obama made his case. From the White House transcript:

The good news is that starting October 1st, new online marketplaces will allow consumers to go online and compare private health care insurance plans just like you’d compare over the Internet the best deal on flat-screen TVs, or cars or any other product that is important to your lives. And you’re going to see competition in ways that we haven’t seen before. Insurance companies will compete for your business. And in states that are working hard to make sure this law delivers for their people, what we’re seeing is that consumers are getting a hint of how much money they’re potentially going to save because of this law. In states like California, Oregon, Washington, new competition, new choices, market forces are pushing costs down.

He pointed out people around him, Dan and Rick and Morgan, who got rebates on their insurance. The law was about them, Obama suggested — despite his opponents' efforts. "I recognize that there are still a lot of folks -- in this town, at least -- who are rooting for this law to fail," he said. "Some of them seem to think this law is about me. It's not. I already have really good health care."

He concluded with a warning about the difficulty of reform.

It’s hard. This is a big country, and the health care industry is massive and there are tons of providers. And so as we implement, there are going to be glitches and there are going to be certain states that for political reasons are resisting implementation. And we're just steadily working through all that stuff.

The same was true when Medicare was started. The same was true when Social Security got started. There were folks who, for political reasons, resisted implementation. But once it got set up, people started saying, this is a pretty good deal; it gives me a little more security. It’s part of that basic bargain that if you work hard, if you're doing the right thing, that you can get ahead in this country -- and that you can provide some basic protections for your family.

Photo: Obama gestures at today's event. (AP)