Three days before the first Republican presidential debate, where Jeb Bush will go head to head with the man who displaced him at the top of the polls for the first time, Bush's campaign released a proposal for immigration enforcement. This is not a coincidence. Bush and his campaign are trying to protect themselves against attacks from the right on immigration, from Donald Trump and basically every other candidate in the race, over his support for legal status for unauthorized immigrants currently in the US.

But simply opposing "amnesty" doesn't automatically secure the border. Bush knows how border security actually works better than the Donald Trumps of the world — he literally wrote a book on it — and this proposal, for the most part, is a more sober, realistic plan for preventing unauthorized migration than his opponents are likely to make.

Instead of making promises that the government can't keep, Bush is focusing on interior enforcement — where the US really could be doing more — instead of border enforcement, where there isn't much more it can do. The takeaway: If you cared more about preventing unauthorized migration than about looking tough, here's what you would do.

Bush believes that comprehensive immigration reform is the best way to prevent unauthorized migration

"Comprehensive immigration reform" is a catchphrase for a three-part policy: increased immigration enforcement both at the border and in the interior of the US, to prevent future unauthorized migration; a way for unauthorized immigrants who are already in the US to stay (usually via a path to legal status and ultimately the ability to apply for citizenship); and reforms to legal immigration. The theory behind the policy is that it's the best way to "secure the border" and end unauthorized migration: it's a lot easier to prevent unauthorized migration than it is to root out 11 million people who've been here for years.

That seems to be what Bush is proposing here, too. The end of his campaign's fact sheet says (emphasis added), "These six proposals, when combined with a rigorous path to earned legal status, would realistically and honestly address the status of the 11 million people here illegally today and protect against future illegal immigration." It's not a full-throated endorsement of the comprehensive immigration bill the Senate passed in 2013, but it's an important note: These proposals aren't supposed to work in a vacuum.

Bush knows that improving immigration enforcement is really about the interior — not the border

A lot of border security proposals, especially from Republicans, are about requiring the Border Patrol to meet quantitative goals — in other words, using metrics to define what a "secure border" looks like. That's not a bad idea, if you can design the right metric. But using the metrics that exist right now would be a disaster. They'd be more likely to lead to Border Patrol cooking the books than to actually improve border security.

Bush and his team are avoiding promises about making the border "100 percent secure" because they know that's not something any president can do right now. And just as importantly, they're avoiding extravagant promises about doubling the Border Patrol or giving it billions more dollars — things that the government could actually do, but that wouldn't actually improve Border Patrol effectiveness that much.

Most of Bush's proposals are in line with what Border Patrol is asking Congress for right now: expanding the use of "forward operating bases" (a tactic Border Patrol's already using to keep agents stationed in remote areas), expanding surveillance technology, building more roads. The one exception: Bush, like pretty much every Republican, wants to deregulate federal park land on the border to make it easier for Border Patrol to maneuver there, but Border Patrol maintains the Department of the Interior already gives it the access it needs.

Politically speaking, the point of talking about things like "forward operating bases" is to remind Republican voters that Jeb Bush actually knows things about immigration policy, unlike some people who might currently be leading in the polls. But as a matter of policy, Bush simply isn't interested in massive border buildups as a show of force, because the US border already has been built up over the last several years, and unauthorized border crossings are very low. Where Bush's more aggressive proposals are is in interior enforcement — something where there is a lot more that could be done.

The part of the plan that would matter: employment and visa enforcement

As the Bush proposal points out (and as Republicans have started acknowledging pretty regularly), at least 40 percent of currently unauthorized immigrants entered the country legally and then overstayed their visas. To catch visa overstays, you don't need more border security. What the Bush plan (like the 2013 Senate bill and other comprehensive immigration reform plans) proposes is that you need a way to track who's left the country on time and who hasn't, and a way to prevent any unauthorized immigrant who does manage to stay in the US from getting a job.

Bush wants a "biometric exit system" — using fingerprints and iris scans to verify which visa-holders are leaving the US. Biometric exit is one of those ideas that sounds great, and because the Obama administration hasn't fulfilled a congressional mandate to implement it yet, it's a good way to bash Obama. But the reason it hasn't been implemented is because, barring a big breakthrough in tech, it would be massively expensive and result in much longer lines at Customs for flights leaving the country.

Furthermore, Marc Rosenblum of the Migration Policy Institute told Vox, the current tracking system (which uses passports) already tells us who's left the country about as effectively as a biometric system would. The problem is finding and apprehending the people who haven't left. The meaningful part of Bush's visa enforcement proposal is to spend more resources on tracking down and deporting people who overstay their visas — which isn't currently a federal enforcement priority.

Bush also wants mandatory E-Verify, which would require employers to check the immigration status of everyone they hire against a federal database. And (almost certainly in response to the killing of Kathryn Steinle in July and the outcry against "sanctuary cities" in Congress) he wants to expand local/federal cooperation on immigration enforcement.

Both of these are enforcement programs, but they're also routinely proposed as part of comprehensive immigration reform proposals. And how they would work depends largely on something Bush is leaving out of this fact sheet: whether current unauthorized immigrants would be able to apply for "earned legal status" while all of these enforcement measures were being implemented, or whether the enforcement would happen first.

If internal enforcement measures are put in place before the 11 million unauthorized immigrants in the US can apply for legal status, it's not at all clear that the enforcement measures would be as effective — it would be a lot harder to know where the government should be directing its enforcement resources, and, as Bush admits, they can't deport everyone. Meanwhile, all those enforcement measures will make life a lot harder for the people Bush wants to get legal status down the road.

Can Bush persuade the GOP that improving security is more important than opposing "amnesty"?

Of course, there's no reason for Bush to go into detail about how legalization fits into his immigration plan right now. The Bush campaign's goal is to remind Republican voters and elites that while Bush might disagree with them on legal status for unauthorized immigrants, he's more serious about securing the border than Donald Trump is.

But Bush's campaign might be in denial about the real political problem the candidate faces. The Republican voters who are most concerned about immigration care about preventing "amnesty" — and they tend to define amnesty as anything that lets unauthorized immigrants stay in the US, whether that's a path to citizenship or a path to legal status. So as long as Bush takes a "pro-amnesty" position, his other arguments may fall on deaf ears.

Bush's campaign probably knows he has no hope of appealing to hardcore amnesty hawks, especially now that they have a candidate (in Donald Trump) who gives voice to their deepest anxieties about immigrants. But for anyone who really does care most about preventing unauthorized migration, Jeb Bush would like you to know that he's your guy.