As reports that Meredith Vieira is planning an exit from NBC's "Today Show" swirl, the anchor has sparked controversy over her failure to question a number of unsubstantiated challenges to the U.S. citizenship of President Barack Obama that Donald Trump floated in an interview with Vieira this morning.

Trump--the billionaire real estate tycoon and reality TV figure who is flirting with a 2012 presidential run--again sought to suggest that Obama was not born in the United States. "Birther" activists on the right have circulated the unsubstantiated claim in an effort to depict Obama's presidency as the outgrowth of a shadowy, constitutionally illegitimate conspiracy.

The birther position has been thoroughly debunked, and it hasn't gained traction within the journalistic mainstream. But Trump has nonetheless been on a media blitz in recent weeks promoting it.

When the issue came up on "Today"--which airs on the same network as Trump's "Celebrity Apprentice"--Vieira didn't exactly hold his feet to the fire."His grandmother in Kenya said he was born in Kenya and she was there and witnessed the birth," said Trump, reiterating a claim that has been proven false, as Vieira sat by silently.

Critics took note."Trump simply steamrolled over her challenges, for instance, on Hawaii's policy as to what birth documents it makes available," writes Time's James Poniewozik.

"But she also let him make the claim that Obama's grandmother said she saw him born in Kenya--an old, and long-debunked, chestnut of birthers that ranks up there with the fake Mombassa birth certificate--without questioning it. So now millions of Today viewers are invited to take it as fact."

NBC quickly followed up with a "Fact Check" segment debunking all of Trump's nonsense:

Of course, the question is: Why couldn't the interviewer have pointed Trump's lies out to him in real time?