Sen. Bernie Sanders, I-Vt., made frequent use of charter flights and laid out highly specific demands to staffers regarding his air travel and hotel accommodations while running for president, according to an excerpt from new book detailing Democratic presidential campaigns ahead of the 2020 election.

Sanders’ habits on the campaign trail were detailed in “Battle for the Soul: Inside the Democrats’ Campaigns to Defeat Trump” by author Edward-Isaac Dovere. In the book, Dovere wrote that private air travel was a “revelation” to Sanders, who had flown commercially before his upstart presidential run in 2016 catapulted him to the national stage.

“Charter flights were a revelation to him. He would always be a little embarrassed pulling into the private terminals, but boy, did he get a kick out of not worrying about being late for a flight that couldn’t take off without him,” Dovere wrote regarding Sanders. “By the beginning of 2017, his staff had put together a document laying out his minimum requirements for the kind of aircraft he’d require if asked to go on trips beyond his regular route back and forth between Vermont and Washington. Couldn’t be too cramped. Couldn’t get too bumpy.”

Sanders was the early frontrunner for the Democratic Party’s nomination to challenge then-President Donald Trump last November, running a campaign that called for universal health care and an end to wealth inequality. A self-declared democratic socialist, Sanders has also expressed support for the “Green New Deal,” an economic and environmental policy overhaul championed by progressives.