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Whether President Barack Obama's health-care overhaul survives could depend on a yin-and-yang pair of conservative Washington, D.C., power lawyers who sued to stop it mere hours after the bill became law in March.

The lawsuit, filed in Florida by David Rivkin and Lee Casey, is one of a handful of challenges lodged against the law in recent months. Like Messrs. Rivkin and Casey's action, some of the suits argue that Congress doesn't have the Constitutional authority to require people to buy health insurance or face a fine, a key tenet of the legislation.

But largely because the Florida lawsuit was lodged on behalf of 20 state attorneys general, it has become the most closely watched case in the ongoing political battle overt the health-care overhaul.

"This is one of the most important Constitutional challenges in history," said Mr. Rivkin, who along with Blaine Winship, an assistant attorney general in Florida, is scheduled to defend the lawsuit in front of U.S. District Court Judge Roger Vinson.