Former President Bill Clinton says his charity has never done anything “knowingly inappropriate” and that he won’t stop giving high-priced speeches because “I gotta pay our bills.”

In an interview with NBC News, the former president said he had no regrets about taking millions of dollars in foreign cash for the Clinton Foundation. The donations have caused a political headache for his wife, Hillary Clinton, who is seeking the Democratic nomination for president in 2016.

A new book, titled “Clinton Cash,” asserts that foreign entities who made payments to the foundation and to former President Clinton through speaking fees got favors from the State Department when Hillary Clinton headed it.

Also read: Book says Hillary Clinton’s State Department did favors for foreign donors.

The Clintons have pushed back against the book’s claims. “There is no doubt in my mind that we have never done anything knowingly inappropriate in terms of taking money to influence any kind of American government policy,” Bill Clinton said in the NBC interview, which aired Monday. “That just hasn’t happened.”

The former president also says he’ll keep giving speeches. A recent New York Times report said Clinton was paid $500,000 for a speech in Moscow from a Russian investment bank with links to the Kremlin. Last year, a Washington Post review of the Clinton family’s financial disclosures found he was paid $104.9 million for 542 speeches around the world between January 2001 and January 2013.

“I gotta pay our bills,” Clinton told NBC. “And I also give a lot of it to the foundation every year.”

While the book has made for unwelcome headlines for her campaign, Hillary Clinton’s standing as the front-runner for the Democratic nomination is solid. She is nearly 50 percentage points ahead of Sen. Elizabeth Warren of Massachusetts in the latest RealClearPolitics average of polls. Warren has insisted she isn’t running for president, but supporters continue to urge her to do so. In the same poll average, Clinton leads Sen. Bernie Sanders — her only official challenger to date — by almost 57 points.