At least two other Tweeters say they heard it too:

https://twitter.com/jsteele220/status/489483221596635136

If Sen. Leahy said it, he wouldn’t be the first. We’ll bring you video as soon as we find it.

Update:

Courtesy of Adam Baldwin, here’s the video.

Related:

Dianne Feinstein uses ‘disgusting comparison’ for illegal immigrants at border