In what may have been a first at a presidential debate, GOP candidates hoping to succeed Barack Obama talked about the H-1B visa Wednesday night. It was largely a missed opportunity.

CNBC moderators aimed their debate questions about the visa program at Sen. Marco Rubio (R-Fla.), who is seeking a major H-1B increase, and Donald Trump, the billionaire who's staked out a position critical of the temporary work visa.

The debate offered Rubio and Trump a chance to contrast their positions. They didn't.

The debates are taking place even as U.S. Sen. Charles Grassley (R-Iowa) is working in the background on a new H-1B bill. Grassley has long advocated restrictions on the visa program in legislation co-sponsored with Sen. Dick Durbin (D-Ill.). Grassley's office confirmed that a new bill is in the works, but officials aren't ready to talk about it.

That bill may be introduced later this year, according to other sources unconnected with Grassley's office.

Rubio, in response to questions last night, said companies that abuse the H-1B program should be barred from it. But he didn't explain, nor was he asked, why he didn't join fellow Florida Sen. Bill Nelson, a Democrat, in asking for an investigation in June of visa workers at Disney Parks and Resort in Orlando. Some Disney IT workers had to train their temporary visa-holding replacements as a condition of severance.

"Does he think the Disney case is abuse?" said Ron Hira, an associate professor of public policy at Howard University.

The visa topic was introduced by John Harwood, CNBC's chief Washington correspondent, who asked Rubio to reconcile his strong support for raising the H-1B cap against the criticisms from his colleague, Sen. Jeff Sessions (R-Al.).

Sessions, as chair of the Senate's immigration subcommittee, has drawn attention to the displacement of U.S. workers by visa holders. Rubio is a co-sponsor of legislation, the I-Squared bill, which would raise the base H-1B cap from 65,000 to 195,000 and eliminate any cap on people who earn advanced STEM degrees at U.S. universities. There is now a 20,000 cap for these students. Rubio believes there is a high-tech skills gap; Sessions does not.

Sessions says that "the tech industry uses this program to undercut hiring and wages for highly qualified Americans. Why is he wrong?" said Harwood.

"Well, first of all, if a company gets caught doing that, they should never be able to use the program again," said Rubio. "If you get caught abusing this program, you should never be able to use it again."

Southern California Edison IT workers were replaced by H-1B visa holders. Ten senators wrote a letter seeking a probe of visa use at the utility. Rubio did not sign this letter.

Rubio continued: "The second thing I said is we need to add reforms, not just increase the numbers, but add reforms. For example, before you hire anyone from abroad, you should have to advertise that job for 180 days. You also have to prove that you're going to pay these people more than you would pay someone else, so that you're not undercutting it by bringing in cheap labor."

A requirement that employers first recruit for 180 days before turning to an H-1B worker is a new proposal by Rubio, who was part of the "Gang of Eight" that shaped the Senate's 2013 comprehensive immigration bill. That bill, which was never voted on by the House of Representatives, included a requirement for 30-day advertising recruitment.

The subsequently introduced I-Squared bill, however, doesn't include a recruitment ad requirement.

Rubio's decision to rail against cheap labor has problems. The 2013 immigration bill did increase prevailing wages for H-1B workers, but only to 80% of the average wage of American workers, said Hira. "That means an employer would be able to get at least a 20% discount by hiring an H-1B," said he said.

Trump wants to raise prevailing wages to the median and impose a requirement that businesses hire Americans first before turning to foreign workers. That's similar to the position Grassley and Durbin have offered up for years, and will likely do so again.

But a question posed by CNBC's Becky Quick to Trump sent the debate off on an odd tangent. "You have been very critical of Mark Zuckerberg of Facebook, who has wanted to increase the number of these H-1Bs," said Quick.

Trump quickly jumped in.

"I was not at all critical of him," said Trump. "In fact, frankly, he's complaining about the fact that we're losing some of the most talented people. They go to Harvard. They go to Yale. They go to Princeton. They come from another country and they're immediately sent out. I am all in favor of keeping these talented people here so they can go to work in Silicon Valley."

Quick was knocked a little off-balance by Trump's response. "Where did I read this?" she asked.

"I don't know," Trump said. "You people write the stuff."

Quick later countered, noting that in the case of Rubio, "I think you called him Mark Zuckerberg's personal senator because he was in the favor of the H-1B"

"I never said that. I never said that," Trump insisted.

On Trump's campaign website you can read exactly what Trump said about the Facebook CEO: "Mark Zuckerberg's personal Senator, Marco Rubio, has a bill to triple H-1Bs that would decimate women and minorities," wrote Trump, detailing his position on increasing prevailing wages for H-1B workers.