"This article by the Sun Times is a deliberate attempt to defame me, and I will sue them immediately," Walsh writes in the letter, which was also sent to his supporters. "My adult children have been my life. I pledged to them two years ago that I would fight these charges privately to keep them out of the news, but with the Chicago Sun Times fabricating a story, I am, at long last, going to fight back."
The original story didn't quote Walsh or his attorney, though it has since been updated to include comments from both after the letter was released early Tuesday morning.
While the letter on Walsh's website includes updates showing the story's changes, its headline threatening a lawsuit and the related paragraphs have not been altered.
Walsh has launched a conservative super-PAC and flirted with the idea of running for governor or senator in 2014, though that has seemed less likely in recent weeks. He is also trying to land a radio deal.