A moderate Republican state senator in Missouri, got so fed up with the religious right high jacking of his party that he switched sides.

RAYMORE, MO. -- Talk about a nasty divorce. In an announcement last month that left Missouri politicos agape, state Sen. Chris Koster, a rising Republican star and chairman of the Senate's GOP caucus, abruptly declared himself a Democrat.

Not only did Koster join the marginalized minority party in Missouri, but he did so with a thundering speech that lambasted his former colleagues as ignoring the needs of their constituents and slavishly following the dictates of "religious extremists."

The former prosecutor denounced several Republican positions he had once supported, such as steep cuts in Medicaid coverage and subsidized family-planning programs.

But Koster reserved his harshest criticism for GOP efforts to overturn a voter-approved constitutional amendment that protects embryonic stem-cell research in Missouri.

"The Republican desire is to criminalize early-stage stem-cell research in our state," Koster said in a speech he repeated three times as he hopscotched across the state. "Go to Boston for your Nobel Prize; come to Missouri for your leg irons. And the Missouri Republican Party not only tolerates this lunacy, but embraces it," Koster said.

Days later, one of his staffers updated his website -- by deleting a photo of Koster shaking hands with Vice President Dick Cheney.

Koster's decision stunned Republicans here in his district just south of Kansas City and across this quintessential swing state. "There's no precedent for it in the state of Missouri," said GOP consultant Paul Zemitzsch.