WASHINGTON (AP) — President Barack Obama ends a fierce yearlong political drama Tuesday by signing into law a landmark health care reform bill that had been seen as impossible just two months ago. Now, he must sell the law's merits to a wary American public.

House and Senate Democrats who backed the bill as well as ordinary Americans whose health care struggles have touched Obama are joining him for the ceremony in the White House East Room. Afterward, they are heading to the Interior Department for an even larger celebration.

The next act begins Thursday, when Obama visits Iowa City, Iowa, where he announced his health care plan as a presidential candidate in May 2007. There Obama plans to talk about how the new law will help lower health care costs for small businesses and families, selling the overhaul to Americans who are deeply divided over the plan.

Republicans united in opposition pledged to repeal Obama's redesign of the health care system, which they criticized as a costly government takeover impacting one-sixth of the U.S. economy.

So-called tea party activists, voters who believe that government spending and influence should be limited, are angry about the new bill and vowing to extract political revenge on those who passed it.

The government "has declared war on our way of life," activist Eric Odom from Nevada said Monday. "It's now time to boot them from office."

In Florida, about 85 tea party groups have about 100,000 members, according to Everett Wilkinson, a leader in the state's movement. A rally was planned in Boca Raton later Tuesday.

Democrats argue that they have delivered on Obama's campaign pledge for change, revamping a system in which the spiraling costs have put health care and insurance out of the reach of many Americans.

After a rancorous debate, the House voted 219-212 late Sunday to send the 10-year, $938 billion bill to Obama. Not one Republican voted for the bill. Some Democrats also voted against it.

The measure, which the Senate passed in December, eventually will extend coverage to 32 million uninsured Americans, reduce federal budget deficits and ban such insurance company practices as denying coverage to people with existing medical problems.

A companion measure sought by House Democrats to make a series of changes to the main bill was approved 220-211. It goes to the Senate, where debate could begin as early as Tuesday. Majority Leader Harry Reid says he has the votes to pass it — though only under special budget rules requiring just 50 votes.

Republicans plan to offer scores of amendments to slow or change the companion measure, which Democrats hope to approve as written and send directly to Obama for his signature.

Even so, the health care debate will likely continue for months as both parties try to use it to motivate their backers to turn out in huge numbers in the November congressional elections. Republicans hope the polarizing issue will help them retake Congress from the Democrats.

Republicans will accuse Democrats of steamrolling into law a plan they say lacks public support and will lead to high taxes and government meddling in personal health decisions. They have already begun a campaign to repeal it, though that will be largely symbolic because it would require a two-thirds Republican majority in the House and Senate to overcome an Obama veto.

Republican-leaning states are already lining up to sue the federal government over the constitutionality of the health care overhaul legislation. Officials in at least 10 states have agreed to file a lawsuit challenging it on grounds it violates state sovereignty by mandating that all Americans have some form of health insurance. Experts say the effort will likely fail because the Constitution states that federal law supersedes state laws, but it will keep the issue alive until Election Day next November.

Obama's yearlong campaign to overhaul health care seemed at a dead end in January, when a Republican won a special election to fill the late Edward Kennedy's Massachusetts Senate seat, and with it, enough votes to prevent the bill from coming to a final vote in the Senate. But the Democrats regrouped, and relentless prodding by House Speaker Nancy Pelosi persuaded enough House members to pass it with a procedure that did not require a 60-vote supermajority in the Senate.

The bill, passed by the House of Representatives on Sunday night, will bring near-universal coverage to a wealthy country in which tens of millions of people are uninsured.

The measure represents the biggest expansion of the U.S. federal government's social safety net since the 1960s, when President Lyndon B. Johnson enacted the Medicare and Medicaid government-funded health care coverage programs for the elderly and poor.

Although the bill does not provide universal health care, it should expand coverage to about 95 percent of eligible Americans, compared with 83 percent today.

Obama has pushed health care as his top priority since taking office in January 2009. Failure would have weakened him and endangered other issues on the president's ambitious domestic agenda, including immigration reform and climate change legislation.

By the end of September — consumers should notice some changes. Among them, insurers would be required to keep young adults as beneficiaries on their parents' health plans until they turn 26, and companies would no longer be allowed to deny coverage to sick children.

A new high-risk pool would offer coverage to uninsured people with medical problems until 2014, when the coverage expansion goes into high gear. The companion bill includes an election-year rebate of $250 later this year for seniors facing high costs for prescription drugs.

By 2014, most Americans will for the first time be required to carry insurance — either through an employer, a government program or by buying it for themselves. Those who refuse will face penalties from the Internal Revenue Service.

Tax credits to help pay for premiums also will start flowing to middle-class working families with incomes up to $88,000 a year, and the state-federal Medicaid program will be expanded to cover more low-income people.

A majority of working-age Americans and their families will still have employer-sponsored coverage. But the number of uninsured will drop by more than half. Illegal immigrants would account for more than one-third of the remaining 23 million people without coverage.