By Rachel Lippmann, KWMU
St. Louis – The opportunity to speak is a thank-you of sorts to Democrat Claire McCaskill.
She was one of Barack Obama's earliest and most vocal supporters. And she helped Obama to a narrow victory in Missouri's presidential primary.
McCaskill said Obama has told her he appreciates her straightforward style. But she admits she's nervous about making the speech.
"I'm not used to giving speeches with Teleprompters, and I'm certainly not used to speaking in front of 21,000 people," McCaskill said.
McCaskill said she'll use her speech to remind viewers how much is at stake in the election.