Her mother is currently in an intensive care unit of a St. Louis hospital, according to The Associated Press. McCaskill has canceled campaign events — largely get-out-the-vote rallies — until the end of the week.

Opponent Rep. Todd Akin's campaign adviser, Rick Tyler, sent well wishes to the candidate and her family.

"It's sad, and we wish her and her mother well, and we send our thoughts and prayers," Tyler said.

Though McCaskill is off the trail, she's not likely to see much of a negative impact from her lull in campaigning. Democratic operatives on the ground across Missouri will take over the get-out-the-vote efforts, knocking on doors and urging Democrats to vote.

She remains up in most polls, the last of which, out earlier this week, put her 6 points ahead of Akin. McCaskill also holds a substantial cash advantage over Akin, with $2.1 million cash on hand at the end of September to the $553,000 posted by Akin.