Missouri law prohibits the losers of party primaries from later filing as write-in candidates for the same office. That means the Republican candidates who lost to Akin last month can't resume their campaigns.
Saint Louis University political scientist Ken Warren said it is "virtually impossible" for write-in candidates to win. Strom Thurmond did it in South Carolina in 1954. But since then, only one Senate candidate has done so: Alaska Sen. Lisa Murkowski won re-election as a write-in two years ago after losing in the Republican primary.
A write-in campaign would also carry a distinct risk: In a three-way Senate race, another Republican could split the vote with Akin, allowing for an easy McCaskill win, Warren said.
Associated Press Writer Jim Salter contributed to this report from St. Louis.
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