The first big public rift in the coalition supporting the Senate Gang of Eight immigration bill is coming to light, per this report from The Hill‘s Alexander Bolton, and it’s predictable enough:

Pro-immigrant advocates are pushing back against the Gang of Eight’s strategy to win 70 votes or more for comprehensive immigration reform, fearing it would require too many concessions to Republicans.

Liberal advocates of comprehensive immigration reform argue the bill only needs 60 votes to clear the Senate and that additional concessions to pad the vote total are not necessary.

Sen. Charles Schumer (D-N.Y.) and other members of the gang are pushing for 70 votes to give it maximum political momentum out of the upper chamber.

But the cost of winning 15 to 17 Republican votes could prove steep. Pro-immigrant advocates are leery of proposed changes to strengthen enforcement provisions, which could lengthen the already arduous path to citizenship for an estimated 11 million illegal immigrants.

Probably the easiest way to look at it is that a 70-vote bill would produce a product closer to the kind of stunted and punitive “reforms” likely to emerge from the House. But that doesn’t really mean “momentum” for the Senate bill; it could just as easily generate additional demands for concessions by House Republicans.

But it’s no accident the biggest champion for additional changes in the Senate bill is Marco Rubio, who is quoted extensively in Bolton’s article. Assuming he has any interest in running for president ever, he needs to narrow the gap between “his” Senate bill and the position of conservatives in and beyond both chambers. Beyond that, the credit he’s due to get from “Establishment Republicans” for dragging his party into an immigration reform effort its base largely despises goes right down the drain if he can’t eventually get a bill enacted, even if it’s a pale imitation of what he professes to favor.

Meanwhile, many Democrats and progressive pro-reform advocacy groups are undoubtedly tired of conservatives being the only ones who get attention and issue demands. Ensuring the “tent” supporting a Senate bill isn’t so big that it’s wide open to the winds is an entirely legitimate goal.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.