After California’s then-Attorney General Kamala D. Harris announced felony pimping charges last year against the two owners of Backpage.com — a classified-ad website that is a hub for sex trafficking and prostitution, one of the men cut a $10,000 check to House Minority Leader Nancy Pelosi’s super PAC.

Mrs. Pelosi’s political action committee, House Majority PAC, has resisted giving the money back, and an aide to Mrs. Pelosi said the California Democrat knows nothing about the contribution.

The uproar over sexual harassment that began with the Harvey Weinstein scandal has intensified the scrutiny of political contributions linked to Backpage, which law enforcement officials say is the chief platform for activities far worse than harassment, including sexual slavery and child prostitution.

Mrs. Pelosi isn’t the only Democrat struggling to deal with the piles of cash that Backpage’s owners spread around to candidates and state Democratic parties over the years.

Even Ms. Harris, a California Democrat who is now a U.S. senator, ducked the issue. Her office wouldn’t respond to repeated emails about Backpage money going to House Majority PAC and other Democratic organizations. – READ MORE