Missouri’s two-term secretary of state, Robin Carnahan, will announce this afternoon that she will NOT seek a third-term, Jeff City sources tell Prime Buzz.

The decision opens a huge hole in the Democratic Party’s statewide lineup. Even though she lost a 2010 U.S. Senate race to Roy Blunt, she was viewed as a prohibitive favorite to win a third term next year.

If she wanted it, that is. And apparently, she does not.

Carnahan, who just turned 50 last month and is a breast cancer survivor, has expressed interest in serving as governor as her father once did. She considered the race in 2008, but ultimately backed away to make room for Jay Nixon.

Her decision comes on the final day of the year’s third quarter. Until now, Carnahan had shown no interest in raising money, and insiders had said her third-quarter report would show little activity.

That has fueled speculation all year long that Carnahan would not run again.

Two Kansas Citians are among those mentioned as possible Democratic candidates for the office: Jackson County Executive Mike Sanders and state Rep. Jason Kander.

“Mike is taking a serious look at making the race for secretary of state,” a Sanders spokesman said.

More as we get it.