The effort to secure the borders and reform immigration law is about to enter a crucial month at the end of which the fate of the bill will almost certainly be known.

The bill as it emerged from the Gang of 8 can probably not pass the Senate and certainly wouldn’t pass the House, nor should it.

But the Gang of 8 draft was only, as Senator Marco Rubio has said repeatedly said, “a starting point.”

A policy and political disaster awaits if a bill emerges from the Senate that cannot generate enough momentum to get even an amended version through the House and into a conference committee. The House will not be able to salvage a badly disfigured bill coming out of the Senate, so key amendments must be made in the Senate or Republicans in the Senate should say no to the effort and do so quickly.

The three key areas for amendment are (1) the border fence; (2) E-Verify; and (3) provisions to study and implement biometric screening and recording of people entering or leaving the United States.

The first fix is the easiest. As Charles Krauthammer told me on my radio show Friday (transcript here), we need “a fence from left to right, from east to west, except obviously the mountainous areas.”

Almost everyone from the center-right knows the truth of what Krauthammer says, and given that he is probably the single most influential commentator on the center-right, it is pure stubbornness for the Senate GOP to refuse to listen to him and scores of others saying the same thing: Build the fence.

Don’t “study” where it should go. Mandate where it should be built, and how it should be built, and when it should be built if any temporary residence permits are to be issued.

If the Senate’s bill does not mandate the construction of a thousand miles or more of double-fencing with an access road –with specified construction design and schedule, with appropriated money and with “notwithstanding any other law” authority to override the various laws like the Endangered Species Act, the Clean Water Act, NEPA etc.—it isn’t serious.

There is no “study” needed here, just resolve to secure the border. If the law mandates that the 1,000 miles of additional fence, built to specification, begins where the current double-sided fencing ends in California and continues east except for breaks where mountainous or ravine-ridden terrain intervenes, the bill will be specific enough with regards to length. Design can also be locked into legislative language. It will need citizen enforcement provisions and, crucially, a provision that ties the issuance of the temporary residence permits to the construction schedule. Thus citizens would be able to oblige the halt of the temporary permits if and when the fence building lagged.

Naysayers who assert this cannot be done need to look at a map of the interstate highway system. Far more difficult tasks than double-sided fencing with access roads have been accomplished again and again in this country. Through mountains and over ravines as well, though such coverage is not necessary here.

These fencing provisions alone would guarantee enormous support in the community from national security conservatives and amendments making E-Verify robust and immediately applicable to all hires would bring along many of the other current critics of the bill.

Senator Jeff Sessions noted on my radio show (transcript here) that biometric screening is the solution to watch lists that are not watched and a visa program that is deeply dangerous to the United States. This is where the technology gap may exist, or the cost of deployment and the impact on economic growth so staggering as to require phasing. Unlike the fence, which is low tech and actually relatively easy to engineer, biometric screening on a vast scale may or may not be immediately available. Here is where a six-month study of options makes sense, but not by the Department of Homeland Security.

Very few people trust the Department of Homeland Security and with four very good reasons, whose names are Umar Farouk Abdulmutallab, Faisal Shahzad and Tamerlan and Dzhokhar Tsarnaev. These are terrorists who began their journeys towards American targets abroad and got to their targets. DHS did not stop them or track them, and DHS should not be the body charged with deciding what is broken in its system and whether biometric testing could fix it.

There will be other amendments offered, and some will no doubt pass, such as explicit guarantees that so-called “chain migration” is under control. There will be plenty of dumb ideas as well, such as the one floated yesterday about obliging every immigrant in the country illegally to appear in federal court to plead guilty in some sort of scheme to avoid the term “amnesty.” The years of law-abiding residence required to apply for a green card and thus for entry onto the path of eventual citizenship might also be extended.

But the Senate is very close if the Democrats are truly interested in securing the border and discouraging employers from hiring post-regularization workers. Having consulted far and wide for a few weeks, Senator Rubio is the natural leader for the push for a series of key amendments, and the GOP members of the Gang of 8 his natural allies in that cause. With a strong dose of common sense and real border security, comprehensive immigration reform can be on its way to the House by the start of summer. Without such amendments, it needs to go back into hibernation until after the 2014 elections.

The Senate GOP cannot send the House a bill that cannot be salvaged. That is policy and political suicide of the sort that wrecks not just careers --though it would surely do that-- but elections as well. May is the month for a decision on whether or not the country will finally secure its border and fix its immigration system or decide to wait again.