The suspense surrounding the Gang of Eight's immigration package now appears to be whether the legislation can garner 70 Senate votes and head to the House with political momentum.

The bill began the week lacking the support of the bare-minimum 60 senators required for passage, looking as though it might be in trouble. But the so-called "border surge" amendment negotiated by two Republican senators -- Tennessee's Bob Corker and North Dakota's John Hoeven -- put a historic comprehensive immigration reform package on the cusp of clearing the Senate.

Besides the four "Gang of Eight" Republicans, five additional GOP senators have sighed on as cosponsors: Kelly Ayotte of New Hampshire; Dean Heller of Nevada; Orrin Hatch of Utah; Lisa Murkowski of Alaska and Mark Kirk of Illinois. Perhaps just as crucial, four Democrats whose support for immigration reform was considered uncertain also are cosponsoring the measure: Sens. Mark Begich of Alaska; Joe Donnelly of Indiana; Joe Manchin of West Virginia and Mark Pryor of Arkansas.

"I believe a large bipartisan vote in this body will change the dynamic in the House," said Sen. Charles Schumer, D-N.Y., a "Gang of Eight" member and Democratic point man in negotiations over the Corker-Hoeven amendment.

For Republican proponents of immigration reform, the battle moves to defending the border security measures in the Corker-Hoeven proposal that engendered the decisive GOP support for the "Gang of Eight" package that would appear to put the bill on a glide path to final passage.