Sen. Bernie Sanders, I-Vt., released 10 years of tax returns Monday evening, showing the majority of his income came from his U.S. Senate salary until 2016, when his income jumped with the publication of a book on his first presidential run.

His total income popped to over $1 million in 2016 and 2017, after he wrote “Our Revolution: A Future to Believe In” in November 2016, raising his effective tax rate for those years to over 30 percent.

“I consider paying more in taxes as my income rose to be both an obligation and an investment in our country,” Sanders said in a statement his campaign released. “I will continue to fight to make our tax system more progressive so that our country has the resources to guarantee the American Dream to all people.”