Rep. Emanuel Cleaver (Mo.), who represents most of Kansas City, also attended the event and spoke before McCaskill.

Biden’s presence at the event underlined President Obama’s support for McCaskill’s re-election. McCaskill took some heat earlier this month when news broke that she planned to skip the Democratic National Convention, with critics suggesting she was trying to avoid being tied too closely to the president. But McCaskill said Obama approved of her decision, calling it the “right thing to do.”

The Missouri Republican Party was happy to tie McCaskill to the Obama administration, noting in a statement from Executive Director Lloyd Smith that she “cast the deciding vote to force Obamacare on the nation and Missouri, and she has voted with the president 95 percent of the time since 2010.”

McCaskill is a top target this year and big money is flooding her state to oppose her reelection. She will face one of three Republicans — Rep. Todd Akin, John Brunner and Sarah Steelman — vying for the nomination in the Aug. 7 Missouri primary.

The Hill rates the race as a "toss-up."

Updated at 7:56 p.m.