WASHINGTON -- The Supreme Court upheld nearly all of President Barack Obama’s healthcare law Thursday, ratifying the signature domestic achievement of his presidency and affirming the broad overhaul that Democrats had sought for more than six decades.

The decision assured that the law will continue to take effect — barring an unexpected repeal — extending coverage to the uninsured, providing new protections such as coverage for pre-existing medical conditions and imposing new taxes to finance it all.

In a ruling that’s politically far-reaching but legally restrained, the court said in a 5-4 decision that Congress had acted within its taxing power when it mandated that people buy health insurance or pay a penalty. The rest of the healthcare law likewise survived, save for tinkers with a provision that directs states to expand Medicaid coverage.

“It is reasonable to construe what Congress has done as increasing taxes on those who … choose to go without health insurance,” Chief Justice John Roberts Jr. wrote for the majority. “Such is within Congress’ power to tax.”

An alliance

Roberts, a 57-year-old conservative nominated by former President George W. Bush, formed an intriguing alliance with the court’s four Democratic-appointed justices to control the decision.

In essence, they reached the same conclusions by different routes. The liberals wanted a more expansive ruling. Instead, they ended up providing most of the votes while Roberts narrowed the reasoning as much as he could.

“I know there will be a lot of discussion today about the politics of all this, about who won and who lost. That’s how these things tend to be viewed here in Washington,” Obama said at the White House after the decision. “Whatever the politics, today’s decision was a victory for people all over this country whose lives will be more secure because of this law and the Supreme Court’s decision to uphold it.”

Congressional Republicans, who voted en masse against the Patient Protection and Affordable Care Act in 2010, vowed to kill it if they could. The House of Representatives will vote on a repeal bill July 11, Majority Leader Eric Cantor, R-Va., announced Thursday. Though the repeal is likely to pass the House, it almost certainly will fail in the Senate, where Democrats hold the majority.

“There’s a lot of resolve amongst our colleagues, and amongst the American people, to stop a law that’s hurting our economy, driving up the cost of healthcare and making it more difficult for employers to hire new workers.,” House Speaker John Boehner, R-Ohio, said in a statement.

Passed on party-line votes in Congress, the law includes hundreds of provisions that are being phased in over several years. Many are politically popular across party lines, such as one allowing parents to keep their children on family insurance policies until the age of 26. The centerpiece, though, is a government mandate on individual Americans that alarms conservatives.

The mandate requires that taxpayers obtain a minimum level of health insurance coverage by 2014. With some exceptions, those who don’t get insurance must pay annual fees that start at $95 in 2015 and rise to $695 by 2016. The court upheld this mandate, though not necessarily in the way many expected.