Politicians serious about immigration reform must tackle caps on visas for new immigrants, border security and the people now in the country illegally, says an immigration law expert.

Lynn Marcus, co-director of the Immigration Law Clinic at the University of Arizona's James E. Rogers College of Law, says the impetus for comprehensive reform is here, with Republicans and Democrats coming to the table.

But whether it comes about depends on three key factors.

"People have been talking for years about how to get to comprehensive reform," Marcus said. "What they're talking about is modifying the system for legal immigration of over, at this point, 1.2 million people a year, about changes to the security and enforcement provisions and something to be done about the 11 to 12 million people in the country illegally."

Current law puts caps on the numbers of foreigners who can migrate to be reunited with their families or to take jobs that go unfilled because there aren't U.S. citizens with the skills and abilities to do the jobs. Those caps should be raised, Marcus says.

Border security has become a euphemism for cutting off immigration, she said.

"Billions of dollars have already been spent trying to secure the border," Marcus said. "I don't know that it's ever going to be secure enough to satisfy some people. So when people say, 'Secure the border first,' to a lot of people, myself included, that's code for, 'Let's not do immigration reform.' The only way to reform the system is to work on all these aspects at the same time."

As for the existing illegal immigrants in the country, "amnesty has become a bad word," Marcus said. She said some are calling for a number of requirements, including civics tests, English proficiency and passage of a criminal background check.

It is not realistic to expect that those in the country illegally will depart and "go to the back of the line" in their own countries to apply for legalization in the United States, Marcus said.

"I hope that there's a reasonable prospect," Marcus said. "There is reason for hope. I'm guardedly optimistic, but as I said before, we have been here before."