Given that his tenure as perhaps America's leading newsman is likely over, let's recall a better time when Williams made a little bit of history for the right reasons: when he hosted the first ever live coverage of NASCAR in 1999.
The first ever live NASCAR race on NBC Sports was a Busch Series (now Xfinity Series) race at Homestead-Miami Speedway, the 1999 HotWheels.com 300. I can't embed the video so click here to watch it.
NBC's first ever live Winston Cup (now Sprint Cup) race came the very next day at the very same track, the 1999 Pennzoil 400.
Williams' passion for stock car racing is well known, even discussing it on Letterman last fall (no, not that Letterman appearance), so him hosting NBC's NASCAR coverage is not a stretch even as it happened only in 1999. One would not expect him to appear on NBC's NASCAR coverage when it makes its return July 4th weekend for obvious reasons.
Also for some context as this came in a different era of NASCAR on television. Before the historic television deal with Fox, NBC and Turner that began in 2001 (and was signed just days before the aforementioned races), the networks made deals directly with the tracks instead of with NASCAR. Therefore by 1999 and then 2000, there were six networks carrying NASCAR Winston Cup races: CBS (which carried the Daytona 500 and other early season contests), ABC, ESPN, TNN (now Spike), TBS and NBC. It may seem foreign to younger NASCAR fans who are used to only two or three networks carrying races, it was not that long ago that NASCAR races could vary greatly on where they aired. Hence why the 1999 television deal was so important and truly showed how big NASCAR had gotten in this country.
So while Williams had suffered a nice, self-inflicted shot to his credibility, at least to NASCAR fans, he will always have Homestead.
*For the interest of disclosure purposes, I should note that I intern with NBC News in Washington.