Vermont Sen. Bernie Sanders’ 2018 re-election campaign spent nearly $300,000 on private jet services in October, a report from the Federal Election Commission shows.

Sanders, a climate change hawk, went on a campaign blitz involving nine states to stump for Democratic candidates ahead of the November midterm elections, according to VTDigger. His aggressive campaigning likely served as a preamble for the independent senator’s potential bid for the 2020 Democratic nomination for president.

Sanders, who flew on private Apollo jets, has already positioned himself highlighting climate change as a major economic, infrastructure, and national security challenge in 2020. His busy travel schedule came the same month he issued a stark warning ahead of the November elections on the planet’s impending doom if humanity remains largely asleep at the wheel combating environmental threats.

“Climate change is the single greatest threat facing our planet,” Sanders said in an Oct. 17 tweet. “On Nov 6th, we must show up at the polls coast to coast and stand with candidates who are willing and ready to accelerate our transition to clean energy, and finally put people before the profits of polluters.”

While private jets are a common tool for political campaigners, the same day the massive check was written to a private jet company, Sanders issued a call to arms to take on greenhouse gas emissions.

“Climate change is a planetary crisis. Our task is clear. We must take on the fossil fuel industry that’s largely responsible for global emissions and accelerate our transition toward energy efficiency and sustainable energy sources,” Sanders wrote in an Oct. 10 tweet.

All flight contributes to humanity's carbon footprint. However, experts and advocates often encourage people to think about their personal carbon footprint, which is why taking public transportation can be less taxing on the environment than driving a car or flying private.

Climate change is likely to be a central issue in the Democratic bout for the 2020 nomination. Sanders potentially faces a large roster of Democrats including former Vice President Joe Biden, Ohio Sen. Sherrod Brown, California Sen. Kamala Harris, and New Jersey Sen. Cory Booker, all of whom have highlighted humanity’s impact on the environment and called for green jobs.