Presidential campaigns are expensive. Mitt Romney spent $44 million of his own money to support his unsuccessful campaign.

But Hillary Clinton may have the largest campaign debt in presidential history, and a big chunk of it is owed to PR mega-firm Burson-Marsteller.

According to the Times' Michael Luo:

Some of Mrs. Clinton's largest outstanding bills are to some of her closest advisers, who might be willing to cut her a deal. Mrs. Clinton, for example, owes nearly $5 million to the firm of her former pollster and senior strategist, Mark Penn.

As Luo notes, it is not uncommon for agencies or consultants to cut deals for their biggest or highest profile clients. We'll see if that is the case with Clinton/Penn.

Meanwhile, Penn wrote an op-ed in this Sunday's Times titled, "The Problem Wasn't the Message - It Was the Money," where he wrote, "While everyone loves to talk about the message, campaigns are equally about money and organization...that simple fact may just have had a lot more to do with who won than anyone imagines."