Senators already earn a sizable salary, but writing about their work turns out to be an effective way to earn some extra cash.
Members of the Senate can earn hundreds of thousands of dollars — in addition to their annual Senate salary of $174,000 — by penning memoirs and other books.
Eleven senators raked in more than $2 million in book royalties or advance payments in 2015, according to financial disclosure reports recently released.
Cashing in on books was a bipartisan affair. Six Democrats and five Republicans earned money for their writings.
Sen. Elizabeth Warren earned the most. The Massachusetts Democrat received a $625,000 payment from publisher Henry Holt & Company. Warren's office did not immediately respond to a request for comment on whether this was related to her 2014 memoir, "A Fighting Chance," or a new book.
Texas Sen. Ted Cruz got the second-highest payment from a publisher. He received more than $476,000 from Harper Collins, which published his book, "A Time for Truth," in June 2015.
And Cruz wasn't the only former Republican presidential contender to make extra bucks on his book.
Kentucky Sen. Rand Paul earned more than $200,000 in royalties, likely from his May 2015 book, "Taking a Stand." Florida Sen. Marco Rubio received more than $100,000 in royalties from the publisher of his 2012 book, "An American Son" and his January 2015 tome, "American Dreams."
New Jersey Democrat Cory Booker got more than $400,000 in royalties for his bestselling book, "United: Thoughts on Finding Common Ground and Advancing the Common Good."
Other senators were on the lower end of the royalties spectrum.
Utah Republican Sen. Mike Lee received more than $34,000 for his book, "Our Lost Constitution."
Senate Majority Leader Mitch McConnell was paid $45,000 for his memoir, "The Long Game" — although the Kentucky Republican's financial disclosure report for next year likely will include further payments, since the book was published in May 2016.
Even senators whose books were published before 2015 still benefited from their past literary efforts. Arizona Sen. John McCain, the 2008 GOP presidential nominee, received more than $4,000 in royalties for his three previous books.
Other senators who earned money for putting pen to paper included Democratic Sens. Barbara Boxer of California, Kirsten Gillibrand of New York, Amy Klobuchar of Minnesota and Claire McCaskill of Missouri.