Lost amid the congressional shouting over immigration reform is a Washington rarity: A freshman Republican with Tea Party roots and scant experience in the national political arena is poised to engineer a legislative feat that eluded more senior lawmakers of both parties for years.

Sen. Marco Rubio, of Florida, sat down with The Washington Examiner to discuss the prospects for an unlikely bipartisan compromise on immigration reform that he helped craft as a member of the Senate's Gang of Eight and which he is now trying to sell to fellow conservatives, the package's most vocal critics.

Sitting in his Capitol Hill office while fellow senators opened debate on the bill last week, Rubio said the compromise still needs tweaking and that he's set to propose specific changes to toughen border security provisions, a key sticking point for Republicans. And even then, Rubio indicated, he may still vote against a bill on which he worked so long.

WEX: Is the debate progressing the way you hoped it would several months ago?

Rubio: We have a bill that covers 95 percent of the bases, but there are some important issues yet to be resolved. And, like any major piece of legislation, when you take it out of the group that helped structure it at the beginning and now expose it to the world — to the entire country and to 92 other senators — you're going to have input, you're going to have changes, you're going to have suggestions, you're going to have ways of looking at it that maybe you haven't thought about, and we're trying to take all of that into account. ... I'm cautiously optimistic.

WEX: How important is it that amendments be allowed and that Senate Majority Leader Harry Reid not cut debate short?

Rubio: It's one of the red lines we outlined at the beginning of this process. We've always said we wanted it to be a part of a fair and open process. ... The vast majority of people in the Republican conference are looking for ways to improve this. And, if you think about what they're asking for, it's not unrealistic and it's not unfair. What they're basically saying is, before we allow people who have violated the laws of the United States to become permanent residents of this country, we want to make sure that we are never going to have a wave of illegal immigration in the future like the ones we had in the past. How is that unreasonable?

It doesn't do us any good to pass a bill out of the Senate that has no chance whatsoever of being anything like what the House is intending to take up; that's another thing that we have to calculate into this.

WEX: What are the biggest challenges facing this bill?

Rubio: There are two challenges that I think are predominant: Benefits and borders. ... No. 1, it's in our organizing principles that people who have violated our immigration laws are not going to benefit from public benefits, and that has to be air tight. ... And, second, is security. We have to make sure that we never have this problem again. And so, the Democrats are asking for certainty on the green card; we're asking for certainty on security, and I think that's a very fair equation.

WEX: Would you still vote for the bill without substantive changes?

Rubio: I want to avoid those kind of ultimatum-red lines at this stage, because I don't think it's constructive to the process. ... My position is very clear, that if this bill doesn't have certain measures, it isn't going to pass, it isn't going to get 60 votes, and I'll say that. ... I'll say this thing is going nowhere, we've wasted our time. We've wasted six months of the Senate's time.

WEX: Do you think the bill has 60 votes?

Rubio: Not only do I not think it; I know it — and so do [the Democrats.]

WEX: Are you going to offer your own border-security amendment?

Rubio: We're prepared to. ... It's critically important that we detail in the bill what the border plan and the fence plan is, because there's just no trust. ... So, what I'm arguing is that we should make that plan detailed. Let's detail what the border plan is, so when members vote for this bill, they're not voting for the promise of coming up with a border plan in the future, they're voting on a border plan that we have seen, that we have talked to border patrol agents about and that we actually know how many miles of fence, how many sensors, how many cameras, what we're actually asking them to complete before the green card process can start.

The second aspect of it that we're going to have to have a debate about is: How can we measure? So, not just input-based. But how do we measure on the back end how the program is working? How do we measure whether it's successfully been implemented?

[The Democrats] don't want anything to make the path to citizenship uncertain. But it already is conditioned. The path to citizenship in this bill — the path to that green card — it's already conditioned on the full implementation of E-Verify [standards for employers]. It's already conditioned on the full implementation of the entry-exit tracking system. And, the last thing is, it's got to be fully conditioned on the completion of the specific border plan that we detail.