(CNN) -- Taxes took center stage in renewed Republican attacks on the Obama administration's sweeping health care legislation Thursday after the Supreme Court rebuffed attempts to derail it based on its constitutionality.
Using the court's finding that the centerpiece of the law -- the individual mandate -- amounted to a legal exercise of congressional tax power became Plan B for the GOP.
"That's not what the president said when he introduced the bill, but what the court said was that it's OK because it's a tax," U.S. Rep. Tom Price, R-Georgia, told CNN. "The debate that we're happy to have is that our friends on the other side of the aisle [not only] want to tax what you do, they want to tax even what you don't do."
And Florida Republican Sen. Marco Rubio said, "Millions of Americans may now have a IRS problem as a result of the ruling."
But Lawrence Jacobs, a leading chronicler of the battle over health care, says that shouldn't be a surprise.
The requirement that all adults have health coverage is the linchpin of the Patient Protection and Affordable Care Act, the health care legislation President Barack Obama signed in 2010 after an epic brawl in Congress. That rule survived its last legal challenge Thursday when the Supreme Court ruled it was constitutional under the legislative branch's power to impose taxes.
Obama had denied the mandate was a tax during a 2009 interview with ABC, comparing it to state requirements that motorists carry auto insurance.
"Nobody considers that a tax increase. People say to themselves, 'that is a fair way to make sure that if you hit my car, that I'm not covering all the costs.' "
At least four million people are expected to pay a tax penalty when the rule takes full effect in 2016, bringing in about $54 billion to help offset the $1.7 trillion, 10-year cost of the act, according to the nonpartisan Congressional Budget Office. But it's only one of several revenue-raising provisions that help pay for the costs of the act, commonly dubbed "Obamacare."
"This was the Democratic tax bill," said Jacobs, a University of Minnesota political scientist and co-author of a 2010 book on the health care battle.
In addition to the mandate, there is a higher Medicare tax rate on taxpayers making more than $200,000 a year or $250,000 for married couples, and it added a tax on investment income to fund the federal health program for seniors.
"It's one of those invisible things, and it's very important," Jacobs said.
There's also an excise tax on so-called "Cadillac" health plans, which had been hotly debated at the time; a higher threshold on medical deductions; and a 10% excise tax on indoor tanning services. But while Republicans have long opposed higher taxes, Jacobs said they concentrated their fire on the mandate instead.
"Rather than getting into a convoluted conversation about taxes that were pretty obscure to most people, they latched onto the individual mandate," he said. "Now that the Supreme Court has up held the mandate, it's really kind of taken the wind out of their sails."
Jacobs said most Americans will be covered by employee health plans, a head of household's employer or by existing government programs such as Medicare, Medicaid or veterans' benefits. Of the roughly 6% of the population remaining, a large portion of those will be exempted from the mandate either because of poverty, religious belief or other reasons, he said.
CNN's Matt Smith contributed to this report.