In what many view as a near deal-killer to the Senate’s massive immigration reform bill, Senators cleared a controversial amendment late Wednesday night to sunset guest-worker provisions in the measure. Sources indicated early Thursday morning that the already delicately crafted deal was on life support heading into today’s expected vote to close off debate. The amendment, sponsored by Sen. Byron Dorgan (D-N.D.), passed the chamber 49-48. It would place a five-year limit on the immigration bill’s provision to allow 200,000 temporary workers per year. If Senators fail to invoke cloture to move toward final passage today, Majority Leader Harry Reid (D-Nev.) must decide whether to pull the measure from the floor — which he has previously said he would — or give it more time. Several Senate sources said some original crafters of the bill were working furiously to try to salvage the measure. — Erin P. Billings