Meet the group persuading states to block Medicaid expansion.

The D.C.-based advocacy group Americans for Prosperity has poured more money and resources than anyone else into convincing Republicans around the country to repel state efforts to grow the federal health insurance program for the low-income and disabled.

It has pelted swing districts with mailers, filled the airwaves with paid advertising, sent volunteers door to door and hosted town hall meetings in a concentrated effort to sway legislators away from approving Medicaid expansion, which is a key way Obamacare extends health coverage to the poor.

The group won't disclose how much money it has spent in total on the effort. But it's "in the millions," says AFP President Tim Phillips.

"From the very beginning, we turned to a state-by-state effort to stop the expansion of Medicaid," Phillips told the Washington Examiner. "Medicaid expansion and Obamacare has been the issue we've worked on more than any other single issue."

His group's success has been striking this year. Attempts to expand Medicaid in Tennessee, Utah, Wyoming, Montana and Idaho — which at first showed promise — have been blocked so far, and now Florida Gov. Rick Scott is showing some new skepticism even though he'd previously supported it.

Obamacare's offer of Medicaid expansion is one of the few parts of the Affordable Care Act that has won some Republicans over. A handful of Republican governors have joined Democrats in growing the program — and accepting the federal money that comes along with it. Twenty-eight states have expanded Medicaid, and more appeared poised at the beginning of 2015 to join them.

But that hasn't exactly panned out, amid AFP's flood of advocacy efforts, all aimed at driving home its message that expanding Medicaid will hurt more than it will help.

Just about every conservative group despises President Obama's healthcare law. But AFP's success in actually getting states to reject one of its central components is largely due to the group's massive and growing network of 34 state chapters and many more local field offices.

In Tennessee, AFP has spent about $300,000 on ads opposing Medicaid expansion, hosted around eight town hall meetings around the state and convinced about 200 local activists to protest at the state capitol wearing red shirts. All six of its full-time staff have been working on the issue this year in some way, according to Tennessee Director Andrew Ogles.

Republican Gov. Bill Haslam had sought GOP support for an alternative Medicaid expansion plan, but the bill died in committee during the legislative session.

"When the governor began talking about it over the holidays, we really had to go into rapid-response mode," Ogles said.

The group has launched aggressive efforts in many other states, too. When Virginia Gov. Terry McAuliffe, a Democrat, took office in 2014 vowing to expand Medicaid, AFP's state chapter ran ads slamming him and noting that it's part of Obamacare.

Besides spending about $350,000 on advertising, the group also says it has knocked on 50,000 doors and made 75,000 phone calls to shift the public towards opposing expansion instead of supporting it.

Part of AFP's strategy is tying expansion to Obamacare, as the healthcare law is generally less popular than Medicaid. States already offered Medicaid prior to the law but can now expand their programs under Obamacare, with the federal government paying for the bulk of new enrollees.

"Join AFP in the fight to stop Obamacare in Tennessee," said one ad funded by AFP. "Obamacare's been a disaster. Expanding Obamacare in Tennessee will be the same."

AFP and other conservatives point out the federal government could withdraw the extra Medicaid funds somewhere down the line, leaving states on the hook to pay for the new enrollees. Obamacare provides that Medicaid can cover people earning up to 138 percent of the federal poverty level.

But proponents of Medicaid expansion — which tend to include major medical associations, hospitals and doctors — note that it gives states a big new infusion of federal dollars and argue that extending health coverage to the low-income will pay off in the long run.

They're frustrated that AFP's efforts in Florida seem to be paying off, where Gov. Rick Scott is now wavering and a majority of House legislators appear to oppose it.

"Scott has aligned himself firmly with the Koch Brothers instead of the veterans, students and hardworking families with no access to healthcare in his state," said Mark Ferrulo, director of Progress Florida.

Florida AFP Director Chris Hudson said his chapter aims to have knocked on 25,000 doors in targeted districts by the end of the week and will keep running radio ads in every market around the state.

"We're going to be doing radio and we're going to be doing mail, quite frankly, until this is all wrapped up," Hudson said.