On Monday, a bipartisan group of eight U.S. senators were all smiles as they unveiled a blueprint for immigration reform. Commentators have been noting that prospects for comprehensive reform are better now than they were when President Bush made several failed attempts in his second term. But one reality has changed that could make things a lot more complicated for the reformers: the passage of Obamacare.

Immigration has long been a divisive issue, not just for the nation as a whole but within the Republican Party and the conservative movement. There's always been a more libertarian strain of thinking that has favored a less restrictive immigration system. These advocates of smaller government have been forced to wrestle with the challenge of how to maintain a more open immigration system given the existence of a generous welfare state.

Milton Friedman, the legendary libertarian economist, famously acknowledged this reality. Ironically, Friedman argued that immigration from Mexico was a good thing -- but only if it was illegal. As he explained, "As long as it's illegal, the people who come in don't qualify for welfare, they don't qualify for Social Security, they don't qualify for all the other myriad of benefits that we pour out from our left pocket to our right pocket."

Confronting this issue prior to 2010, libertarian-minded folks had a ready response -- immigrants come to this country to work, not collect welfare, and most of them are going to be too young to qualify for old-age benefits anyway.

But after the March 2010 passage of Obamacare, the issue isn't quite so simple. Obamacare isn't an entitlement aimed at benefitting those who don't work -- its target beneficiaries are the working poor. Through an expanded Medicaid program and new subsidized insurance exchanges, the law will provide benefits to those earning up to four times the federal poverty level.

Relative to the population as a whole, immigrants are more likely to work in jobs that don't provide health insurance coverage. By 2022, assuming full implementation of Obamacare, more than a quarter of the overall uninsured population will be "unauthorized immigrants," according to the most recent Congressional Budget Office data. This is a population of about 8 million.

Under current law, the federal government is expected to spend $254 billion, insuring 36 million through Obamacare in 2022. Adding 8 million newly eligible individuals to the mix would boost that number by $57 billion in that year alone, assuming the per capita cost remains constant. That could translate to hundreds of billions of dollars in increased costs over the course of a decade.

Anticipating this, framers of the bipartisan compromise stipulate that "current restrictions preventing nonimmigrants from accessing federal public benefits will also apply to lawful probationary immigrants." "Probationary status" is what would be given to qualifying illegal immigrants when the plan is approved. A White House fact sheet on President Obama's proposal echoes this: "Consistent with current law, people with provisional legal status will not be eligible for welfare or other federal benefits, including subsidies or tax credits under the new health care law."

But it's unclear that the law as currently written would actually prevent newly legalized immigrants from accessing such benefits. In outlining the requirements for the exchanges, for instance, the legislative text of Obamacare references "alien(s) lawfully present in the United States" as being eligible.

Alex Conant, a spokesman for Sen. Marco Rubio, R-Fla., one of the leading backers of the bipartisan Senate proposal, said that lawmakers still needed to work out the legislative details, but he emphasized there was an agreement in the general principle regarding benefits.

Of course, even a deal to prevent those given probationary legal status from accessing Obamacare wouldn't apply to those who eventually do become citizens.

Republican proponents of immigration reform, who have fought Obamacare tooth and nail, may be forced to confront an uncomfortable reality: Immigration reform has the potential to represent a major de facto expansion of Obamacare. If the issue isn't satisfactorily addressed once details are fleshed out, it could derail any potential compromise.

Philip Klein (pklein@washington examiner.com) is a senior editorial writer for The Washington Examiner. Follow him on Twitter at @philipaklein.