How can this be legal?

Voting on Obamacare - by not voting on it. [Link]

Pelosi (D-Calif.) would rely on a procedural sleight of hand: The House would vote on a more popular package of fixes to the Senate bill; under the House rule for that vote, passage would signify that lawmakers "deem" the health-care bill to be passed.
The tactic -- known as a "self-executing rule" or a "deem and pass" -- has been commonly used, although never to pass legislation as momentous as the $875 billion health-care bill. It is one of three options that Pelosi said she is considering for a late-week House vote, but she added that she prefers it because it would politically protect lawmakers who are reluctant to publicly support the measure.
"It's more insider and process-oriented than most people want to know," the speaker said in a roundtable discussion with bloggers Monday. "But I like it," she said, "because people don't have to vote on the Senate bill."