The Supreme Court delivered President Obama a pivotal victory Thursday in upholding his health care law, the signature legislative accomplishment of his first term, but only after declaring its financing mechanism a tax on Americans.

Obama will address the ruling later Thursday, according to administration officials.

The president is expected to celebrate the ruling as a validation of his policies while highlighting some of the law’s most popular provisions, including a requirement that insurance companies cover
people with pre-existing conditions.

(See more photos from the Supreme Court)

Republican Mitt Romney and Republicans will use the decision as a rallying cry for ousting Obama in the fall campaign.

“Today’s Supreme Court decision sets the stakes for the November election,” Republican National Committee Chairman Reince Priebus said. “Now, the only way to save the country from ObamaCare's budget-busting government takeover of health care is to elect a new president.”

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(View the Supreme Court's ruling)

Romney has promised to overturn the law if elected president.

"If it is deemed to stand then I'll tell you one thing," Romney said earlier, "we're going to have to have a president, and I'm that one, that's going to get rid of Obamacare, and we're going to stop it on
day one."

In the weeks leading up to the ruling, Obama defended the law even as he expressed doubts that the largely conservative court would uphold it.

"It's the right thing to do to give seniors discounts on their prescription drugs," Obama said. "It's the right thing to do to give 30 million Americans health insurance that didn't have it before."