In a speech to supporters, Sanders thanked the people of New Hampshire for his victory – as he looked ahead to the November election.
“Let me say tonight that this victory here is the beginning of the end for Donald Trump,” Sanders said.
In 2016, Sanders was reportedly the 19th-poorest U.S. senator, according to The Washington Post. However, he has since published four books, and that's said to have helped make him a millionaire.
"I wrote a best-selling book," Sanders told The New York Times in April. "If you write a best-selling book, you can be a millionaire, too."
That money comes, in part, from his book royalties and his income as a senator, which pays him $174,000 a year, according to the Congressional Research Service report on Senate salaries last year.
Sanders also receives an annual pension from his time as the mayor of Burlington, Vermont, and owns three homes, according to Forbes.
He has a home in Burlington, a home in Washington, D.C., and a Vermont vacation home that he and his wife bought in 2016 a few months after his presidential campaign ended.
After receiving pressure to release his tax returns during his presidential bid, Sanders released 10 years' worth of returns on April 15 this year, which is also tax day.
According to those returns, the independent Vermont senator's adjusted gross income was $561,293 in 2018 and he paid a 26 percent effective tax rate. In 2017, his adjusted gross income was $1,131,925.
“These tax returns show that our family has been fortunate," Sanders said when he released the documents. "I am very grateful for that, as I grew up in a family that lived paycheck to paycheck and I know the stress of economic insecurity."