To hear Sen. Charles Schumer tell it, lawmakers crafting an immigration reform bill will focus on two big tasks. "First, defining metrics that demonstrate that the border is secure," the New York Democrat explained at a Jan. 31 news conference. "Second, defining exactly what the path to citizenship looks like and how it proceeds."

For Schumer and some Senate colleagues, that is the short version of immigration reform: first, border security, and second, a path to citizenship.

But immigration reform as envisioned by the so-called Gang of Eight is actually a three-step process. Schumer left out the first part: immediate legalization of the estimated 11 million illegal immigrants in the country. In the statement of principles released by the gang on Jan. 28, legalization begins the process, followed by securing the border, and then, after an as-yet-undefined standard of border enforcement is met, a path to citizenship.

It's the first step, immediate legalization, that worries skeptics. Those worries intensified after Schumer and others gave varying accounts of how they expect it all to work.

When the Gang of Eight rolled out its proposal, Schumer spoke openly about immediate legalization. "On day one of our bill, the people here without status who are not criminals or security risks will be able to live and work here legally," he said. "Immediately when the bill passes, people who are here living in the shadows would get a legal right to stay here and work. They would no longer be deported, provided they don't have a criminal record. They would no longer be harassed. They would be working ... the ability to stay here and work and stay in America and not be deported or harassed comes virtually immediately."

Two days later, at a forum sponsored by Politico, Schumer added emphasis: "People immediately can get a work visa, so they're out of the shadows, they can work, they can stay in the United States if they don't have a criminal charge against them."

Soon critics began to point out flaws in the Gang of Eight scheme. Conservative columnist Charles Krauthammer called immediate legalization "the functional equivalent of a green card" and "the very essence of amnesty." Blogger Mickey Kaus called the proposal "a giant incentive for people to come here illegally." And the Manhattan Institute's Heather Mac Donald wrote that it gives illegal immigrants "the immeasurable advantage of legal presence in the U.S. while waiting for their green card, unlike aliens obeying the law and waiting in their own country for permission to enter."

In later appearances, Schumer and fellow Democrats began to speak less of immediate legalization and more of a two-part, enforcement-then-path-to-citizenship process. But their demeanor suggested their hearts aren't in any plan based on strong enforcement.

"We want the border to be secure," Schumer said at that Jan. 31 news conference. "But we're not using border security as an excuse or block to the path of citizenship."

Later, Senate Majority Leader Harry Reid, appearing on ABC's "This Week," was asked whether the final immigration deal would include what Gang of Eight member Sen. Marco Rubio, R-Fla., calls "operational control" of the border. "I don't know what that means, and I don't think he does either," Reid responded. "The fact is we have some metrics we're talking about, some numbers. And we can do that. But this legislation is going to pass."

The message: Reid is determined to push immigration reform through the Senate, whatever is happening along the border.

The majority leader and his fellow Democrats are vague about enforcement because it's not the key to their plan. The key is immediate legalization. In the Gang of Eight scenario, enforcement will be preceded -- not followed by, but preceded -- by legalization. After that happens, the process will be impossible to stop.

When Schumer says, "We want to make sure that employers do not hire people who are here illegally," he knows immediate legalization will make that point moot. Employers won't hire people who are here illegally because nobody will be here illegally; they'll all have been legalized by the Gang of Eight's plan.

As far as border security is involved, members of the Gang of Eight are proposing reinstituting electronic security measures that have already failed. And those inadequate measures would go into effect as the prospect of immediate legality lures more people to cross the border illegally.

Immediate legalization is the very heart of the Gang of Eight proposal. It is likely to be at the heart of conservative and Republican opposition to the Gang of Eight plan. And if the fragile alliance between Democrats and Republicans falls apart, it will likely be the cause.

Byron York is chief political correspondent for The Washington Examiner.