By COREY BOLES

WASHINGTON—Mitt Romney and congressional Republicans on Thursday pledged a renewed effort to repeal the Obama administration's health-care overhaul, undeterred by the Supreme Court ruling to uphold the law's central tenet.

How will today's Supreme Court decision on health care play out on the presidential campaign trail? Jerry Seib on Lunch Break has details.

The high court ruled 5-4 that the health law's penalty for those who ignore a mandate to carry health insurance counted as a tax and was justified by Congress's constitutional taxing power.
"What the court did not do, I will do on my first day as president," the presumptive Republican presidential nominee said, asserting that the policy amounted to a tax increase on Americans.
"What the court did today was say that Obamacare does not violate the Constitution," Mr. Romney added. "What they did not do was say that Obamacare is good law, or that it's good policy. Obamacare was bad policy yesterday. It's bad policy today."
As Democratic lawmakers celebrated, minutes after the ruling was announced Thursday, GOP leaders in Congress said the battle isn't over.
"Today's ruling underscores the urgency of repealing this harmful law in its entirety," said House Speaker John Boehner (R., Ohio). "Republicans stand ready to work with a president who will listen to the people and will not repeat the mistakes that gave our country Obamacare."
The Republican leader in the Democratic-controlled Senate echoed Mr. Boehner's call to repeal the law, saying it hurts the private sector.
"Today's decision makes one thing clear: Congress must act to repeal this misguided law," said Senate Minority Leader Mitch McConnell (R., Ky.). "Obamacare has not only limited choices and increased health-care costs for American families, it has made it harder for American businesses to hire."
Republicans routinely use the term "Obamacare" to deride the administration's health-care law.
House Majority Leader Eric Cantor (R., Va.) said GOP leaders would bring a bill to the House floor the week of July 9 to repeal the health-care law. Shortly after Republicans took control of the House in the wake of the 2010 midterm elections, House lawmakers voted along party lines to repeal the law. Such efforts haven't gone far with a Senate and White House controlled by Democrats.
Democrats were ebullient, once it was clear which way the court ruled on Thursday morning.
Democratic Sen. Richard Durbin (D., Ill.) was in the middle of signing the conference report on a major highway bill when an adviser read out a news alert from his BlackBerry saying the law's key individual mandate provision had been ruled unconstitutional, today's equivalent of the erroneous "Dewey Defeats Truman" headline in 1948. The misleading news alert was quickly followed by accurate headline that the mandate had been upheld.
Senate Majority Leader Harry Reid (D., Nev.) on Thursday called the law "the greatest single step in generations for ensuring access to affordable quality health care for every person in America, regardless of where they live or how much money they make."
Speaking on the Senate floor shortly after the decision was released, Mr. Reid also quickly conceded that the law wasn't perfect and said lawmakers would work to improve it next year.
"We know that when we come back here after the elections, there may be some things we need to do to improve the law and we'll do that working together," Mr. Reid said.
House Democratic leader Nancy Pelosi of California, who shepherded the 2010 law through the House, said the decision is a "a victory for the American people" that will lead to "greater accountability for the insurance industry."
In an election year, candidates for the Senate also weighed in quickly on the decision. Mark Neumann, a conservative Republican running for the Senate in Wisconsin said the decision underscored the need to strip Democrats of their majority in the Senate. "The Supreme Court's faulty decision today means we have to elect conservatives to the Senate this fall to end Obamacare and eliminate the individual mandate," Mr. Neumann said.
At least one moderate Republican reacted with more reflection than some in the conservative branch of the party.
Rep. Steve LaTourette (R., Ohio) said that "it's great that the system works—I think people are surprised that the chief justice was the deciding vote, but I do think it puts to rest this notion that he was going to be a rubber stamp for Republican ideology."
—Naftali Bendavid, Janet Hook and Siobhan Hughes contributed to this article.Write to Corey Boles at [email protected]