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. (You can watch the exchange in the clip above.)

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."

A spokeswoman for the "Today Show" did not respond to a request seeking comment on whether Vieira felt that she had adequately pressed Trump on his claims. But judging by how some of her peers in TV news have handled Trump in the same situation, she appears to have failed.

Take, for instance, conservative Fox News host Bill O'Reilly, who had Trump on his prime time show several weeks ago, and was well prepared to spar with his guest on the birther issue.

"There were two announcements the week [Obama] was born [in his native Hawaii] in both Honolulu newspapers saying that he was born. That is impossible to make happen if he had not been born in the hospital," said O'Reilly, incredulously. "What is he, baby Jesus? There was a sophisticated conspiracy to smuggle that baby back into the country?"

Vieira, meanwhile, is said to be ready to abandon her anchor chair at "Today." TV Guide reported Tuesday that the host is expected to leave the show when her contract expires later this year. Items reporting the same development swiftly followed in the Hollywood Reporter and the New York Times.

NBC News pushed back on those reports--and a separate one claiming that Vieira's co-host, Matt Lauer, is also on his way out the door--via the network's own internal news service.

"There seems to be an awful lot of speculation around news anchors these days, and it's not our practice to comment on any of it," the network said in a statement.

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