“Obamacare” looks increasingly inevitable, but one lawsuit making its way through the court system could pull the plug on the sweeping federal health care law.

A challenge filed by the Pacific Legal Foundation contends that the Affordable Care Act is unconstitutional because the bill originated in the Senate, not the House. Under the Origination Clause of the Constitution, all bills raising revenue must begin in the House.

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The Supreme Court upheld most provisions of the act in June, but Chief Justice John G. Roberts Jr. took pains in the majority opinion to define Obamacare as a federal tax, not a mandate. That was when the Sacramento, Calif.-based foundation’s attorneys had their “aha” moment.

“The court there quite explicitly says, ‘This is not a law passed under the Commerce Clause; this is just a tax,’” foundation attorney Timothy Sandefur said at a Cato Institute forum on legal challenges to the health care act. “Well, then the Origination Clause ought to apply. The courts should not be out there carving in new exceptions to the Origination Clause.”

With momentum building toward the completion of a draft immigration bill, Republican lawmakers -- even one at the center of the talks -- are urging Senate leaders to slow the process down to avoid making "fatal" mistakes. 

Advocates for a comprehensive immigration reform bill were jubilant over the weekend after representatives for big business and labor agreed on a framework for allowing low-skilled workers into the country. 

Sen. Chuck Schumer, D-N.Y., declared Sunday that "every major policy issue has been resolved," and said he anticipates a bill on the floor as early as May. 

It comes after Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., in a comment Republicans took as a signal the chairman intends to rush the bill through, stressed that his committee has already held dozens of hearings.