KANSAS CITY, Mo. -- For Missouri Sen. Jim Talent, his position against a state ballot initiative to protect embryonic stem cell research isn't political -- it's personal.

"I cannot support a constitutional amendment with a right to clone," Talent told KMBC's Micheal Mahoney in a telephone interview Tuesday.

Despite his opposition, the Missouri Republican is not urging other Missourians to vote one way or another. He said that's a decision voters have to reach on their own.

But his likely Democratic opponent for the Senate, State Auditor Claire McCaskill, said Talent is just trying to "muddy the waters" on a tough issue.

Talent said his long-awaited decision Monday to oppose the measure was the result of a lengthy personal reflection, not based on the impact it could have on his re-election bid.

"Most people don't want the issue to be viewed politically," Talent said in an interview Tuesday. "I don't think they want their political leaders making the decision based on that."

Talent had come under pressure from McCaskill to take a position on the proposed constitutional amendment. The measure specifically bans human cloning, but would permit all federally allowed stem cell research in the state.

The issue has created a rift among Missouri Republicans. Business and medical leaders strongly support the measure while religious and anti-abortion leaders have campaigned against it, saying the procedure amounts to human cloning.

Talent, a longtime abortion opponent, issued a carefully worded statement Monday saying he "personally" could not support the initiative because "this measure would make cloning human life at the earliest stage a constitutional right." At the same time, Talent did not urge voters to reject the measure, but asked them to "make up their own minds on this very difficult moral issue."

McCaskill said Talent's comments "continue to straddle" the issue.

"I don't think you can have the luxury of calling an issue personal or political just to muddy the waters when a tough issue comes along," McCaskill said Tuesday.

"To me this isn't that complicated," she said. "I support this research, I have consistently and enthusiastically, and I urge Missourians to do the same."

"Life does not begin in a petri dish. Life begins in a womb," McCaskill told KMBC.

Rick Hardy, associate professor of political science at the University of Missouri-Columbia, said Talent is doing the best he can under the circumstances to walk a fine line between the different GOP camps.

"He's signaling to his pro-life base that he's not abandoning them, but he understands the complexity of the issue by encouraging people to vote their conscience on this," Hardy said.

Talent's announcement came after stem cell proponents on Monday turned in nearly twice the number of signatures needed to get the initiative on the ballot this fall. Recent polls show Missourians favor the measure by a 2-1 margin.

Earlier this year, Talent withdrew as a co-sponsor of a Senate bill that would ban all embryonic stem cell research and impose a $1 million fine and jail sentence on violators. At the time, Talent said he backed another form of research -- called altered nuclear transfer -- that would not result in human cloning.

Talent's effort to find a compromise angered anti-abortion groups and drew derision from Democrats who accused him of flip-flopping. Some medical experts said Talent's middle ground proposal was not a practical option.

This week, abortion opponents have praised Talent for coming out against the ballot measure, even if he is not asking Missourians to do the same.

"The senator has clearly studied the intentionally misleading language of the initiative and seen the truth," said Jaci Winship, executive director of Missourians Against Human Cloning.

Talent, meanwhile, denied McCaskill's assertions that he is having trouble making up his mind.

"When I decided a year ago to review this, I really believed that the way to go was to reach a personal decision and just stick with that in whatever context and sort of let the politics of it fall wherever it would fall," Talent said.