Marco Rubio has received plenty of attention – and criticism – for skipping Senate hearings and votes as he campaigns for his White House bid.

But this isn’t the first job where Rubio has taken heat for failing to go all in. Documents and records obtained by NBC News suggest that as a visiting professor at Florida International University, he worked less than 10 hours a week and missed three-in-10 classes during his first semester of teaching – all while making more than most part-time visiting professors.

Rubio taught in various capacities at the university from 2008 through April of last year, coming on-board just as he was term-limited out of his position as speaker of the Florida House.

He began his teaching at the school as a Visiting Distinguished Service Professor at the Metropolitan Center, the school’s urban think tank. That position entailed co-teaching two classes with longtime friend and pollster Dario Moreno, as well as “conducting research, assisting with recommendations and developing a proposal for a demonstration project on affordable housing,” according to a release announcing his hire at the time.

For that, he would earn $69,000 — a salary that Moreno told the Miami Herald at the time was considerably more than the $52,000 another part-time visiting professor at the center was making.

It was a salary that raised eyebrows among some FIU professors, prompting questions at an FIU Faculty Senate meeting late last year.

“How do we justify paying him as much as we do to teach one course?” asked Amy Paul-Ward, an associate professor in the Nicole Wertheim College of Nursing and Health Sciences, according to the FIU student paper. “I know there are qualified adjuncts in our school who we have trouble paying $3,000 to teach a course.”

According to his office, from August of 2008 – November of 2009, Rubio raised approximately $125,000 for the Center — enough to cover his salary and then some. A sizeable chunk of that, $100,000, came from Norman Braman — the wealthy auto magnate who’s been a longtime benefactor to Rubio, is helping to bankroll his campaign and whose charitable foundation employs Rubio’s wife.

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Moreno said in an email to NBC News that the course was entirely new, and thus took significant time to prepare.

“We had to prepare 28 new lectures for this new prep,” he said, noting that it usually takes him “3 to 4 hours to prepare a completely new lecture,” and that he’s actually taking time off of teaching next semester to prepare a few new courses for the year.

And in a 2012 deposition obtained by NBC News, Moreno acknowledged that whether Rubio “would devote the necessary time” to the job was a question for administrators while they initially considered whether to offer him the postion.

“We knew he was very charismatic, but we also wanted to make sure that he had the time to put into this effort,” he said.

Moreno added that Rubio’s “a busy person” and he wondered “whether he would devote the necessary time for it.”

But in that same deposition, Moreno himself acknowledges that Rubio put in less than 10 hours per week of work on the course. Asked to estimate how many hours over the course of the semester Rubio spent “actually teaching and as well as planning the course,” Moreno replies, “there was planning ahead of the course — maybe 10, 15 hours of planning.”

“Then there was probably you know, teaching, it’s 3 hours a week. And then he probably put in another 6 hours in preparation,” Moreno added. In a later email to NBC News, Moreno said he meant six hours of preparation per week, as that’s how long it takes him to prepare a new course, but “you need to ask the senator how long it took him to prepare.”

The deposition was part of an ethics investigation in response to a complaint concerning his credit card use, FIU employment and consulting work. It was ultimately dismissed, and Rubio’s office noted that the complaint was filed by a Democratic donor.

But in it, Moreno also states that Rubio attended just 70 percent of the classes they taught together that first semester, though he could only recount the reason for his absences for four of 28 classes.

“There might have been one day where he had to go to Tallahassee [the Florida capital] for something,” he said. “But I think he missed two days because of the Republican convention and then one day because his mother was sick.”

And though Rubio helped prepare the tests for the class, Moreno said during the deposition, “I didn’t let him do any of the grading,” joking that, “he’s still a politician, and I was afraid he was going to give everyone A’s!”

Moreno’s deposition also raises questions about Rubio’s later years at FIU, during which his salary was much lower — at just $24,000 per year. But as a sitting senator, his schedule was much busier.

His pay was first reduced to $40,000 in late 2009, as his run for Senate picked up; after he won that race, he moved to a part-time teaching position at FIU’s School of International and Public Affairs and a further reduced salary of $24,000.

In that position, Rubio co-taught a class that met for two hours and 40 minutes each week; pay stubs from 2011-2013 show him working anywhere from 40 to 15 hours per week, though his biweekly pay remained consistent. It’s a notable chunk of time for anyone juggling Senate, family and campaign demands — let alone a rising young GOP star who sought out a lead role in the 2013 immigration reform effort and campaigned for GOP candidates nationwide in 2014 before launching a run for president.

Rubio’s aides push back against the suggestion his busy schedule would’ve made the time commitment of a part-time professorship difficult, noting while he’s been in the Senate, the courses were scheduled for Mondays and Fridays, when the Senate is typically on break.

And Rubio’s official spokesman, Alex Burgos, noted Rubio received high marks from former students and co-teachers — and that even some formerly critical professors came around to Rubio’s hiring eventually.

"There's a reason FIU asked him to come back year after year. They clearly felt he was providing a great value to the students. The only people who ever seem to have a problem with any of this are Marco's political opponents and some members of the media,” Burgos said.