The fight over the initiative has resulted in millions of dollars spent on commercials and billboards and lawn signs, as well as a massive grassroots effort involving churches throughout the state. Both sides complain that the other has lied to advance its cause.

Nobody knows what impact it will have on the Senate race, considered to be the closest in the nation. Will moderate Republicans who support stem cell research vote for McCaskill because they are unhappy with Talent's position? Will Catholic and evangelical voters turn out in large numbers to oppose the initiative and also vote for Talent?

What does seem clear is that Republicans are deeply divided.

"There are a lot of Republicans who feel strongly that these cells in a petri dish are the equivalent of a person and there are other Republicans who feel that these cells in a dish not implanted in a mother are not the equivalent of a person," said former Sen. John Danforth, R-Mo., the influential senior statesman of Missouri politics and a leader in the fight for stem cell research.

Danforth's brother, Donald, died of ALS in 2001.

"When you see somebody you love suffer and die from one of these diseases, and medical researchers say this could be the key to finding the cure, then you want the researchers to go forward so other people won't go through the same experience."

Danforth said he has met many Republicans who refuse to vote for Talent because of his opposition to the research as well as his opposition to the ballot initiative.Danforth would not say how he will vote in the Senate race.

"On the one hand, this is an exceptionally important issue for me. I cannot overemphasize how important this issue is," he said after a long pause. "On the other hand, I try to be loyal to my party to maintain my credentials within the party to hopefully change it from within."

Terry Jones, a political science professor at the University of Missouri St. Louis, said Talent's loss of some moderate Republicans is likely to be outweighed by the religious conservatives who are stirred by the issue to go to the polls.

"It's a very minor factor in the voters' decision about the Senate race," Jones said.

John Hancock, a former executive director of the Missouri Republican Party, said the issue is unlikely to determine who wins the Senate race because voters will be focused on the ballot question when thinking about stem cell research.

"The reality is that the voters are going to decide the policy at the polls," he said. "If the policy was dependent on the outcome of the Senate race, it would potentially have more impact on people's votes."

To Fox, however, the outcome of the Missouri race, and other congressional contests, does matter.