Bill Keveney

USA TODAY

NBC's Meet the Press has a new moderator: Chuck Todd.

NBC News president Deborah Turness announced the chief White House correspondent's appointment in an internal memo to staff Thursday, shortly after David Gregory posted on Twitter that he would be leaving the program and NBC.

The switch in moderators is not surprising. Rumors of a change have swelled recently, coinciding with a decline in ratings for the Sunday political talk show, the longest-running program on network television.

Todd will take over the show on Sept. 7. NBC News veteran Andrea Mitchell will moderate the program on Sunday and will "continue to be a central figure of the broadcast," as will some others whose names will be announced shortly, Turness wrote.

In the memo, Turness first thanked Gregory, who took over Meet the Press in December 2008, a few months after the death of long-time moderator Tim Russert. Gregory is leaving the network after two decades.

"Under his leadership the show has had a string of exclusives, and David has shown a remarkable gift for holding leaders to account and getting answers on issues that matter to our audience," Turness wrote. "He is an outstanding journalist whose sharp intellect and quick sense of humor have made him a pleasure to work with."

She praised Todd in announcing his new assignment. Todd continues as NBC News political director, but relinquishes his duties as the network's chief White House correspondent and as the anchor of MSNBC's The Daily Rundown.

"There is no one with a bigger passion for politics than Chuck. His unique ability to deliver that passion with razor-sharp analysis and infectious enthusiasm makes him the perfect next generation moderator of this beloved broadcast," she wrote. "Chuck will ensure that Meet the Press is the beating heart of politics, the place where newsmakers come to make news, where the agenda is set."

Turness added that staff would soon be informed of "exciting plans to evolve and update the broadcast under Chuck's leadership."

In his earlier announcement, Gregory tweeted: "I leave NBC as I came – humbled and grateful. I love journalism and serving as moderator of MTP was the highest honor there is."

He continued with a second tweet, expressing appreciation to his colleagues and to viewers. "I have great respect for my colleagues at NBC News and wish them all well. To the viewers, I say thank you."

Rumors of Gregory's possible ouster have risen as the show's ratings have declined. In the TV season to date, Meet the Press is down 5% and 6%, respectively, in viewers and in adults 25 to 54, the primary news demographic.

Its Sunday talk competitors have generally fared better during the same time frame. ABC's This Week with George Stephanopoulos is up significantly (14% in viewers and 15% in adults 25 to 54), CBS' Face the Nation is up slightly (1% in both categories); and Fox News Sunday is up in viewers (3%) but down in adults 25 to 54 (-9%).

On Sunday, which was Gregory's most recent broadcast, Meet the Press finished third in both viewers (2.4 million) and adults 25 to 54 (747,000). It trailed Face the Nation (2.9 million viewers and 772,000 adults 25 to 54) and This Week (2.6 million viewers and 829,000 adults 25 to 54) in both categories.