Sen. Marco Rubio (R-Fla.) (Alex Wong/Getty Images) Sen. Marco Rubio (R-Fla.) (Alex Wong/Getty Images)

In a significant step forward for comprehensive immigration reform, the Senate Judiciary Committee, after wading through hundreds of amendments, passed the Gang of Eight’s immigration plan with the help of Republican Sens. Lindsey O. Graham (S.C.), Jeff Flake (Ariz.) and Orrin G. Hatch (Utah).

True to their word, the Democrats did not insert poison-pill provisions. In the end Sen. Patrick J. Leahy (D-Vt.) chose not to advance his amendment to include same-sex marriage within the bill’s definition of marriage. In a similar move yesterday, Sen. Charles E. Schumer (D-N.Y.) tamped down Democratic objections to measures aimed at preventing illegal immigrants from accessing federal benefits. Likewise, Sen. Richard J. Durbin (D-Ill.) relented on opposition to expansion of H1-B visas, a bugaboo of Big Labor but an essential element to getting Hatch on board. In an era in which nothing gets done by bipartisan horse-trading, it was a remarkable achievement, and one certain to rile immigration exclusionists.

In a statement after the vote, Sen. Marco Rubio (R-Fla.) observed:

I appreciate the work of the Senate Judiciary Committee in taking the bill my colleagues and I introduced in April as a starting point for debate and making improvements to it over the past few weeks. Through an extensive, open and transparent process, they have made real improvements to the bill.

The amended bill that heads to the Senate floor would make significant progress to secure our borders, make E-Verify mandatory for the first time in American history, effectively crack down on immigrants who overstay visas, and modernize the legal immigration system to meet America’s 21st century economic needs for both highly skilled talent and guest workers to fill labor shortages.

And he strongly suggested that the process of bringing Republicans on board was not at an end. (“We have a historic opportunity to end today’s de facto amnesty and modernize our immigration system to meet our 21st century needs. I remain optimistic that the Senate, by improving the bill through an open and deliberative floor debate, will seize this opportunity.”)

On an appearance on CNBC, Rubio was pushing for more assurances on border control. (“Here’s what people are saying — a lot of conservatives: ‘We are prepared to deal with the 11 million that are here now, because we know that they’re never going to go back, the vast majority of them. We’re prepared to deal with that, but only if we take measures that ensure that we don’t have a future wave of illegal immigration.’ I think that’s a very reasonable request, a very reasonable position, and one that I think we need to be able to accomplish if we want this to become a law.”)

Soon it will be time for other Republican senators to show their hands. A Capitol Hill source familiar with the thinking of Sen. Bob Corker, R-Tenn., told me that he was still conducting “due diligence,” but, based on the progress so far, he’s “optimistic that we have an opportunity to do something that is productive for our country.” The source hastened to add that the “details matter.”

Almost as important as the Judiciary Committee’s vote was the announcement from Minority Leader Sen. Mitch McConnell (Ky.) that he would not block the bill from reaching a floor vote: “With regard to getting started on the bill, it’s my intention — if there is a motion to proceed required — to vote for the motion to proceed so we can get on the bill and see if it we’re able to pass a bill that actually moves the ball in the right direction.”

The ground has shifted on the right significantly since 2007 when immigration reform opponents sunk George W. Bush’s effort at comprehensive immigration reform. Now, behind the effort is a significant alliance of fiscal conservatives, evangelicals and forward-looking GOP activists who view immigration as essential to creating a more viable GOP (Bush reached 44 percent support from Hispanics, a figure almost unimaginable today) Many of the stars in the party (Rubio, Rep. Paul Ryan of Wisconsin, New Jersey Gov. Chris Christie, New Mexico Gov. Susana Martinez) are also behind the bill.

This doesn’t, by any stretch of the imagination, ensure passage of the bill, especially in the House. There, with safely gerrymandered districts, a core of stringent conservatives opposed to any form of immigration reform that can pass will seek to disable the bill at every turn. The anti-immigration forces are loud but small and disorganized, having lost the argument with the majority of Republicans (who, polls show, favor a bill like the Gang of Eight’s plan). The bill has a real chance of passage.

But that is down the road for now. The immediate task for Rubio and his compatriots in the Gang of Eight is to hold and expand their coalition in the Senate. They got a big boost Tuesday.

UPDATE: In a significant, positive move for immigration proponents Sen. John Cornyn (R-Tex.) announced that he will vote to bring the bill to the floor. His spokeswoman e-mailed me: “He said last night that he will vote yes on the Motion to Proceed  to the bill. He is hopeful that his amendments will be accepted and improve the bill.” Look for more pro-border-enforcement measures on the floor to pull in Cornyn and a batch of other Republicans.