The grind of the presidential campaign trail is tough--even for the hardiest of candidates. The constant stream of airplanes and buses and drab hotel rooms can make any White House hopeful delirious.

But while The Donald is jet setting on Air Trump, cost-conscious Marco Rubio's campaign is bottom feeding on Frontier, and none are too pleased.

Rubio’s campaign manager Terry Sullivan told reporters Monday at National Review’s 2016 Campaign Managers event at Google’s Washington, D.C. headquarters that flying Frontier was “a special kind of hell.” 

The National Review reports that the Florida senator is running a particularly thrifty campaign that focuses on ways to boost his poll numbers, which means private jets are rare.

“Marco flies 95 percent commercial,” Sullivan said at the event. (The other 5 percent is private.) “We just booked a Frontier Airlines flight today, which is a special kind of hell for anybody. But we do it because we gotta — we want to spend our money where it matters.”

We have no specifics on why flying Frontier was “hell” for the Rubio camp. We reached out to them to elaborate and are awaiting comment.  

But the ultra-low-cost airline isn’t exactly known for its stellar track record.  According to a recent Air Travel Consumer Report from the U.S. Department of Transportation, the airline's complaint rate for July was more than triple the norm for 13 major U.S. airlines—coming in second-to-last place – besting only Spirit Airlines.

Frontier president Barry Biffle, who took control of the carrier last August, acknowledged that they had a lot of things to change when he took the job, but now they're starting to see progress.  He noted that the airline's on-time departures are improving, and in August less than 1 percent of scheduled flights were canceled and customer complaints were down, year over year by 10 percent.

"We’re running a great airline.  And we’ve got some of the best prices in the industry, so I am not shocked that Rubio is using us," he said.

He also said that the airline has a new pricing bundle called The Works, which includes one carry-on bag, priority seating, best available seating and no change fees, which has become a popular cost-saving option.

Rubio, however, isn’t the only candidate flying commercial.  Jeb Bush, after seeing his poll numbers drop, has had to dip into donor funds and cut back on private jets to campaign events.  On Monday, Wisconsin Gov. Scott Walker cited lack of funds as a reason he suspended his presidential bid, and last week former Texas Gov. Rick Perry withdrew from the race, also for money reasons.

Rubio’s camp says that its fiscal discipline will give the senator a competitive edge, but whether it includes flying Frontier in the future waits to be seen.