Most attempts at comprehensive immigration reform have failed in the past, not because conservatives refused to assimilate those who came here illegally into the country. In fact, in the 1986 plan signed by President Reagan, nearly 2.7 million illegal immigrants were allowed to stay in the country. In the proposed 2007 plan, George W. Bush and many congressional Republicans were prepared to accept millions more.

No, the reason many conservatives are justifiably wary of calls for reform is this: The promised border security has never become reality. So today I will discuss the “verify” element essential to any deal on immigration reform.

As a matter of both national security and immigration policy, it is absolutely essential that we both secure our border and modernize our visa system so we know who comes and who goes on travel, student and other temporary visas.

Right now, we basically have no idea: No idea who crosses our border; no idea who overstays a student visa; no idea whether or not a migrant worker leaves as scheduled. In fact, we don’t even know how many migrant workers use the temporary guest worker program, because it is such a mess that very few actually even try.

If our party needs to be honest with ourselves — it is physically impossible and probably more than a little morally wrong to say you will deport 12 million people — then the other party must be honest with themselves too. It is just as wrong is to ask for those 12 million to be assimilated while allowing another 12 million or more to line up to cause the same problem over the next few years. That’s why I have some specific proposals that I believe must be met before conservatives can support immigration reforms.

First ensure operational control of our border. This will mean more boots on the ground, more surveillance and more equipment along our border. It need not mean a physical fence, but in some cases that works best, for instance near high population areas. In other areas a virtual or electronic “fence” may work best. In still others, electronic surveillance may be sufficient.

The securing of our border must contain specific and definable goals. These metrics have been under development for years by the Department of Homeland Security. It is time to implement them. Among the many are: surveillance of the border, fence crossings, numbers caught and released from ICE courts.

There would be border-crossing data gathered by motion sensors; cameras; fence cuttings (when there is physical evidence a person has crossed a fenced portion of border); observational data from Border Patrol and state/local law enforcement; drug and contraband seizures; logging and tracking the frequency of repeat border offenders; visa overstays; tracking of when people cross out of the United States over land (which we do not currently do).

Under my plan, which I will offer as an amendment to any comprehensive immigration reform bill, the border would have to be provably secure, as measured by the above criteria, as certified by the administration and an independent auditor, based upon the metrics in the law. It will be the most robust border security ever enacted.

But I will add one very important, extra protective measure: Congress would have to vote to certify the border was secure, both initially and every year thereafter. It is not enough to let an administration often hostile to the rule of law determine if our border is secure.

This would have to happen before one green card was issued to allow someone to stay in this country who had come here illegally. And if at any time the border is not deemed secure or our systems are not up to tracking the comings and goings of those on visas, all aspects of the reforms will cease.

Border security is not the only measure necessary for successful implementation of reform. Along with border security, we must also prove we have the capacity to do background checks and issue and track visas. According to the State Department, in 2012 we issued 8.9 million non-immigrant visas and 482,000 immigrant visas from outside the United States, and we don’t do it all that well. In order to process the 12 million people under consideration, we need to provably modernize the system and prove it can track the current workload for one year, then be scaled to the future workload. This also must be certified by Congress.

If we can’t secure our border, and if we cannot prove we can modernize our system of issuing and tracking visas, we cannot take on the task of adding more people to the system.

Previously, those who took on immigration reform did so in good faith. They expected the border security they were promised but never received. They hoped for efficient systems to better handle the program.

They got neither. We cannot allow this to happen again.

I share the goal of a working immigration system, and a new approach to allowing those here in our country who want to work and stay out of trouble to stay here. But I will not repeat the mistakes of the past when vague promises were made and not kept.

That’s why I take this stand today. A stand that says I am willing to work with those who seek reform, but one that says you must produce a plan that allows this issue to be fixed once and for all.

Sen. Rand Paul, Kentucky Republican, is a member of the Senate Foreign Relations and Homeland Security committees.