The Senate Judiciary Committee’s markup of a comprehensive immigration rewrite took an emotional and tense turn Tuesday evening when Chairman Patrick J. Leahy, D-Vt., sought to offer an amendment to expand the bill to gay and lesbian couples.

Leahy brought up his measure knowing that Republican senators already had said the amendment would break the delicate “gang of eight” coalition backing the larger immigration reform effort.

It was the final amendment discussed before the panel voted, 13-5, to send the bill to the floor.

Leahy challenged GOP members of the committee, and especially Lindsey Graham of South Carolina, a member of the bipartisan negotiating group that forged the underlying bill.

While Leahy got Graham to concede that the measure under consideration would not affect the marriage laws in South Carolina, the Republican senator still drew a bright line.

“You’ve got me on immigration. You don’t have me on marriage,” Graham told Leahy. “If you want to keep me on immigration, let’s stay on immigration.”

But it was likely the Democrats who caused Leahy to withdraw his proposal to allow Americans to sponsor their foreign-born partners for green cards. Supporters of gay rights pleaded with Leahy to refrain on holding what would have likely turned out to be a hugely embarrassing vote for both him and them.

Gang of eight member Sen. Charles E. Schumer, D-N.Y., appeared visibly upset as he explained that he believed the amendment deserved to be included, but that he would have to vote against it to preserve his deal with Republican sponsors of the bill.

“As much as it pains me, I cannot support this amendment if it will bring down the bill,” Schumer said.

“I’m a politician,” Schumer added, in explaining what he called one of the most difficult decisions of his career.

Similarly, bill sponsor Sen. Richard J. Durbin, D-Ill., argued, “This is the wrong moment. This is the wrong bill.”

Other Democrats, including Sens. Dianne Feinstein of California and Al Franken of Minnesota, indicated they, too, would oppose the amendment to ensure that the rest of the bill would not collapse as GOP supporters withdrew.

The chairman sat with his arms crossed, clearly frustrated in what he viewed as an inevitable but unsatisfactory outcome.

“I take the Republican sponsors of this important legislation at their word that they will abandon their own efforts if discrimination is removed from our immigration system,” Leahy said. “So, with a heavy heart, and as a result of my conclusion that Republicans will kill this vital legislation if this anti-discrimination amendment is added, I will withhold calling for a vote on it.  But I will continue to fight for equality.”

Shortly thereafter, Leahy voted “aye” and the bill passed out of committee.