Senate negotiators have clinched a deal that would double the number of patrol agents and double the length of fencing along the U.S.-Mexico border, giving the Senate immigration reform bill a major boost. Sens. Bob Corker (R-Tenn.) and John Hoeven (R-N.D.) announced the agreement Thursday afternoon and predicted it could secure the votes of as many as 15 Republicans for final passage. The amendment is expected to cost more than $30 billion, and members of the Gang of Eight expressed confidence it would help achieve 100 percent border surveillance and a 90 percent apprehension rate of illegal entrants along the southern border. “Certainly, securing the border should not be an issue if this amendment passes,” Corker said. “If this amendment can pass, I think it will add tremendous momentum to the bill.” “This is about securing the border first. To get comprehensive immigration reform right, we’ve got to first secure the border. That’s what this legislation does. Number one, we require a comprehensive southern border strategic plan. We put that right in the legislation,” Hoeven said. The Corker-Hoeven amendment would double the number of border patrol agents from 20,000 to 40,000 and authorize the construction of 700 miles of fencing along the southern border, twice as much as authorized in the base bill. They plan to introduce the measure on the Senate floor Thursday afternoon. Lawmakers were vetting details of the legislation shortly after lunchtime. Sen. Marco Rubio (R-Fla.) in a separate interview said it would dramatically improve border security. “If you look at what’s being proposed here, this is a dramatic expansion and improvement in border security that I hope will allow finally for this legislation to have the support it needs,” he told Fox News. Corker and Hoeven said Rubio played an active role in negotiating the border security amendment. At the National Hispanic Prayer Breakfast on Thursday, Vice President Biden said it was "essential" for the country "to defend its borders." “But it’s time we pass fair — firm but fair — reforms to bring these 11 million undocumented immigrants out of the shadows,” he said, according to CNN. “The last 10 yards are by far the hardest. They really are. This is the tough, tough time.” The legislation would also guarantee a base level of funding for various border security technologies, such as infrared sensors and drones. “We took all of the ideas that Department of Homeland Security had, added to it, put it right in the legislation so people know what it is,” Hoeven said. “This adds to it and requires it be done and we spell it out so there ’s no confusion.” Sen. John Cornyn (R-Texas) and other lawmakers had been pushing for even tougher language, however, and it is unclear whether the new language will bring along enough Republicans to win the bill more than 70 votes. The Senate on Thursday voted 54-43 to table an amendment from Cornyn that would have put in place mandatory border security triggers. Under the Cornyn "Results" amendment, the border enforcement standards in the underlying Gang of Eight bill would have had to be met before any immigrants could be granted legal status. Cornyn said he was surprised the Gang of Eight agreed to such a large expansion of border patrol agents. “I was told we don't need more boots, we need technology. Now I find to my shock and amazement the distinguished senior senator from Arizona saying we need 20,000 more border patrol,” he said on the Senate floor. A group of conservative GOP senators held a press conference to criticize the Corker-Hoeven plan for not requiring fully operational control of the southern border before granting a pathway to citizenship to an estimated 8 million illegal immigrants. “I think this amendment is designed to pass the bill, but not to fix the bill,” said Sen. David Vitter (R-La.). “I say the amendment is designed that way for two reasons. First of all, as has been noted, it’s all about inputs. There’s no metric, there’s no measure of actual achievement." Vitter argued that Washington is good at spending money but not good at achieving results and “there’s no requirement from what we understand of this Corker-Hoeven amendment of any results.” Sens. Chuck Grassley (R-Iowa), Jeff Sessions (R-Ala.), Ted Cruz (R-Texas) and Mike Lee (R-Utah) also spoke out against the amendment. Conservative policy advocacy group Heritage Action, which has repeatedly criticized the Senate measure, said the Corker-Hoeven amendment would "fail to solve the enforcement problems in the underlying bill." "Heritage Action opposes any amendment that fails to take a security-first approach, including Schumer-Corker-Hoeven, and reserves the right to include any and all as key votes on our legislative scorecard," the group said. Sens. Charles Schumer (D-N.Y.) and Lindsey Graham (R-S.C.), two members of the Gang of Eight, have both set 70 votes as a target to build momentum in the House, where the prospects for immigration reform are tougher. Schumer has worked with Corker and Hoeven on the security measure. The tentative deal did appear to win over centrist GOP Sen. Mark Kirk (Ill.) , who on Thursday said once it was adopted, he would "be proud to vote for a bill that secures our border and respects our heritage as an immigrant nation." Sen. Dean Heller (R-Nev.) also signaled his support by joining Corker and Hoeven at a press conference. “I’ll tell you a lot of us wouldn’t have come along if these two guys didn’t work as hard as they did to put this package together,” said Heller . “I’ve signed onto this amendment.” Corker on Thursday said he thought the language would help convince House Republicans to support the bill. “For people who are concerned about border security, once they see what is in this bill, it is almost overkill,” he said. “I think if that's the issue people have, I think everyone working together has come up with a way to deal with that issue,” Corker said on MSNBC. “I do hope we can send it over to the House with some momentum.” The plan does not include the biometric entry-exit system at border crossings and airports that Republicans had hoped for, and responsibility for designing a border security plan remains with the Department of Homeland Security, not Congress, though the department will be required to submit their finalized plan for approval. The bill is also expected to include a trigger mechanism requiring the implementation of certain border security measures before a pathway to citizenship is made available to the nation's 11 million illegal immigrants. That's been a key stumbling block for many Republicans, but the exact design of the trigger remains unknown. Read more: http://thehill.com/blogs/blog-briefing-room/news/306739-reports-senators-reach-tentative-deal-on-border-security-#ixzz2WnRwICir Follow us: @thehill on Twitter | TheHill on Facebook